Integrate the Google Play Billing Library into your app

This topic describes how to integrate the Google Play Billing Library into your app to start selling products. Before reading this topic, be sure you've set up your Google Play configuration beforehand by following the steps in Getting ready.

This topic includes code examples that are based on the official sample apps on GitHub. See additional resources for a complete list of sample apps and other resources that you can use while integrating.

Life of a purchase

Here's a typical purchase flow for a one-time purchase or a subscription.

• Show the user what they can buy.
• Launch the purchase flow for the user to accept the purchase.
• Verify the purchase on your server.
• Give content to the user, and acknowledge delivery of the content. Optionally, mark the item as consumed so that the user can buy the item again.

Subscriptions automatically renew until they are canceled. A subscription can go through the following states:

• Active: User is in good standing and has access to the subscription.
• Cancelled: User has cancelled but still has access until expiration.
• In grace period: User experienced a payment issue, but still has access while Google is retrying the payment method.
• On hold: User experienced a payment issue, and no longer has access while Google is retrying the payment method.
• Paused: User paused their access, and does not have access until they resume.
• Expired: User has cancelled and lost access to the subscription. The user is considered churned at expiration.

Purchase tokens and Order IDs

Google Play tracks products and transactions using purchase tokens and Order IDs.

• A purchase token is a string that represents a buyer's entitlement to a product on Google Play. It indicates that a Google user is entitled to a specific product that is represented by a SKU. You can use the purchase token with the Google Play Developer API.
• An Order ID is a string that represents a financial transaction on Google Play. This string is included in a receipt that is emailed to the buyer. You can use the Order ID to manage refunds in the used in sales and payout reports.

Order IDs are created every time a financial transaction occurs. Purchase tokens are generated only when a user completes a purchase flow.

• For one-time products, every purchase creates a new purchase token. Most purchases also generate a new Order ID. The exception to this is when the user is not charged any money, as described in Promo codes.
• For subscriptions, an initial purchase creates a purchase token and an Order ID. For each continuous billing period, the purchase token stays the same, and a new Order ID is issued. Upgrades, downgrades, replacements, and re-sign-ups all create new purchase tokens and Order IDs.

For subscriptions, note the following:

• Subscription upgrades, downgrades, and other subscription purchase flows generate purchase tokens that must replace a previous purchase token. You must invalidate the purchase tokens that appear in the linkedPurchaseToken field of the Google Play Developer API. For more information, see Implementing linkedPurchaseToken correctly to prevent duplicate subscriptions.
• Order numbers for subscription renewals contain an additional integer that represents a specific renewal instance. For example, an initial subscription Order ID might be GPA.1234-5678-9012-34567 with subsequent Order IDs being GPA.1234-5678-9012-34567..0 (first renewal), GPA.1234-5678-9012-34567..1 (second renewal), and so on.

Error Handling

The Google Play Billing Library returns errors in the form of BillingResult. A BillingResult contains a BillingResponseCode, which categorizes possible billing-related errors that your app can encounter. For example, if you receive a SERVICE_DISCONNECTED error code, your app should reinitialize the connection with Google Play. Additionally, a BillingResult contains a debug message, which is useful during development to diagnose errors.

Connect to Google Play

The first step to integrate with Google Play's billing system is to add the library to your app and initialize a connection.

Add the Google Play Billing Library dependency

Add the Google Play Billing Library dependency to your app's build.gradle file as shown:

dependencies {
    def billing_version = "4.0.0"

    implementation "com.android.billingclient:billing:$billing_version"
}

dependencies {
    val billing_version = "4.0.0"

    implementation("com.android.billingclient:billing:$billing_version")
}

If you're using Kotlin, the Play Billing Library KTX module contains Kotlin extensions and coroutines support that enable you to write idiomatic Kotlin when using the Google Play Billing Library. To include these extensions in your project, add the following dependency to your app's build.gradle file as shown:

dependencies {
    def billing_version = "4.0.0"

    implementation "com.android.billingclient:billing-ktx:$billing_version"
}

dependencies {
    val billing_version = "4.0.0"

    implementation("com.android.billingclient:billing-ktx:$billing_version")
}

Initialize a BillingClient

Once you've added a dependency on the Google Play Billing Library, you need to initialize a BillingClient instance. BillingClient is the main interface for communication between the Google Play Billing Library and the rest of your app. BillingClient provides convenience methods, both synchronous and asynchronous, for many common billing operations. It's strongly recommended that you have one active BillingClient connection open at one time to avoid multiple PurchasesUpdatedListener callbacks for a single event.

To create a BillingClient, use newBuilder(). You can pass any context to newBuilder(), and BillingClient uses it to get an application context. That means you don't need to worry about memory leaks. To receive updates on purchases, you must also call setListener(), passing a reference to a PurchasesUpdatedListener. This listener receives updates for all purchases in your app.

private val purchasesUpdatedListener =
   PurchasesUpdatedListener { billingResult, purchases ->
       // To be implemented in a later section.
   }

private var billingClient = BillingClient.newBuilder(context)
   .setListener(purchasesUpdatedListener)
   .enablePendingPurchases()
   .build()

private PurchasesUpdatedListener purchasesUpdatedListener = new PurchasesUpdatedListener() {
    @Override
    public void onPurchasesUpdated(BillingResult billingResult, List<Purchase> purchases) {
        // To be implemented in a later section.
    }
};

private BillingClient billingClient = BillingClient.newBuilder(context)
    .setListener(purchasesUpdatedListener)
    .enablePendingPurchases()
    .build();

Establish a connection to Google Play

After you have created a BillingClient, you need to establish a connection to Google Play.

To connect to Google Play, call startConnection(). The connection process is asynchronous, and you must implement a BillingClientStateListener to receive a callback once the setup of the client is complete and it’s ready to make further requests.

You must also implement retry logic to handle lost connections to Google Play. To implement retry logic, override the onBillingServiceDisconnected() callback method, and make sure that the BillingClient calls the startConnection() method to reconnect to Google Play before making further requests.

The following example demonstrates how to start a connection and test that it's ready to use:

billingClient.startConnection(object : BillingClientStateListener {
    override fun onBillingSetupFinished(billingResult: BillingResult) {
        if (billingResult.responseCode ==  BillingResponseCode.OK) {
            // The BillingClient is ready. You can query purchases here.
        }
    }
    override fun onBillingServiceDisconnected() {
        // Try to restart the connection on the next request to
        // Google Play by calling the startConnection() method.
    }
})

billingClient.startConnection(new BillingClientStateListener() {
    @Override
    public void onBillingSetupFinished(BillingResult billingResult) {
        if (billingResult.getResponseCode() ==  BillingResponseCode.OK) {
            // The BillingClient is ready. You can query purchases here.
        }
    }
    @Override
    public void onBillingServiceDisconnected() {
        // Try to restart the connection on the next request to
        // Google Play by calling the startConnection() method.
    }
});

Show products available to buy

After you have established a connection to Google Play, you are ready to query for your available products and display them to your users. To query Google Play for in-app product details, call querySkuDetailsAsync(). Querying for SKU details is an important step before displaying your products to your users, as it returns localized product information. For subscriptions, ensure your product display follows all Play policies.

When calling querySkuDetailsAsync(), pass an instance of SkuDetailsParams that specifies a list of product ID strings created in Google Play Console along with a SkuType. The SkuType can be either SkuType.INAPP for one-time products or SkuType.SUBS for subscriptions.

To handle the result of the asynchronous operation, you must also specify a listener which implements the SkuDetailsResponseListener interface. You can then override onSkuDetailsResponse(), which notifies the listener when the query finishes, as shown in the following example:

suspend fun querySkuDetails() {
    val skuList = ArrayList<String>()
    skuList.add("premium_upgrade")
    skuList.add("gas")
    val params = SkuDetailsParams.newBuilder()
    params.setSkusList(skuList).setType(SkuType.INAPP)

    // leverage querySkuDetails Kotlin extension function
    val skuDetailsResult = withContext(Dispatchers.IO) {
        billingClient.querySkuDetails(params.build())
    }

    // Process the result.
}

List<String> skuList = new ArrayList<> ();
skuList.add("premium_upgrade");
skuList.add("gas");
SkuDetailsParams.Builder params = SkuDetailsParams.newBuilder();
params.setSkusList(skuList).setType(SkuType.INAPP);
billingClient.querySkuDetailsAsync(params.build(),
    new SkuDetailsResponseListener() {
        @Override
        public void onSkuDetailsResponse(BillingResult billingResult,
                List<SkuDetails> skuDetailsList) {
            // Process the result.
        }
    });

The Google Play Billing Library stores the query results in a List of SkuDetails objects. You can then call a variety of methods on each SkuDetails object in the list to view relevant information about an in-app product, such as its price or description. To view the available product detail information, see the list of methods in the SkuDetails class.

Before offering an item for sale, check that the user does not already own the item. If the user has a consumable that is still in their item library, they must consume the item before they can buy it again.

Before offering a subscription, verify that the user is not already subscribed.

Launch the purchase flow

To start a purchase request from your app, call the launchBillingFlow() method from your app's main thread. This method takes a reference to a BillingFlowParams object that contains the relevant SkuDetails object obtained from calling querySkuDetailsAsync(). To create a BillingFlowParams object, use the BillingFlowParams.Builder class.

// An activity reference from which the billing flow will be launched.
val activity : Activity = ...;

// Retrieve a value for "skuDetails" by calling querySkuDetailsAsync().
val flowParams = BillingFlowParams.newBuilder()
        .setSkuDetails(skuDetails)
        .build()
val responseCode = billingClient.launchBillingFlow(activity, flowParams).responseCode

// An activity reference from which the billing flow will be launched.
Activity activity = ...;

// Retrieve a value for "skuDetails" by calling querySkuDetailsAsync().
BillingFlowParams billingFlowParams = BillingFlowParams.newBuilder()
        .setSkuDetails(skuDetails)
        .build();
int responseCode = billingClient.launchBillingFlow(activity, billingFlowParams).getResponseCode();

// Handle the result.

The launchBillingFlow() method returns one of several response codes listed in BillingClient.BillingResponseCode. Be sure to check this result to ensure there were no errors launching the purchase flow. A BillingResponseCode of OK indicates a successful launch.

On a successful call to launchBillingFlow(), the system displays the Google Play purchase screen. Figure 1 shows a purchase screen for a subscription:

Google Play calls onPurchasesUpdated() to deliver the result of the purchase operation to a listener that implements the PurchasesUpdatedListener interface. The listener is specified using the setListener() method when you initialized your client.

You must implement onPurchasesUpdated() to handle possible response codes. The following example shows how to override onPurchasesUpdated():

override fun onPurchasesUpdated(billingResult: BillingResult, purchases: List<Purchase>?) {
   if (billingResult.responseCode == BillingResponseCode.OK && purchases != null) {
       for (purchase in purchases) {
           handlePurchase(purchase)
       }
   } else if (billingResult.responseCode == BillingResponseCode.USER_CANCELED) {
       // Handle an error caused by a user cancelling the purchase flow.
   } else {
       // Handle any other error codes.
   }
}

@Override
void onPurchasesUpdated(BillingResult billingResult, List<Purchase> purchases) {
    if (billingResult.getResponseCode() == BillingResponseCode.OK
        && purchases != null) {
        for (Purchase purchase : purchases) {
            handlePurchase(purchase);
        }
    } else if (billingResult.getResponseCode() == BillingResponseCode.USER_CANCELED) {
        // Handle an error caused by a user cancelling the purchase flow.
    } else {
        // Handle any other error codes.
    }
}

A successful purchase generates a Google Play purchase success screen similar to figure 2.

A successful purchase also generates a purchase token, which is a unique identifier that represents the user and the product ID for the in-app product they purchased. Your apps can store the purchase token locally, though we recommend passing the token to your secure backend server where you can then verify the purchase and protect against fraud. This process is further described in the following section.

The user is also emailed a receipt of the transaction containing an Order ID or a unique ID of the transaction. Users receive an email with a unique Order ID for each one-time product purchase, and also for the initial subscription purchase and subsequent recurring automatic renewals. You can use the Order ID to manage refunds in the Google Play Console.

Processing purchases

Once a user completes a purchase, your app then needs to process that purchase. In most cases, your app is notified of purchases through your PurchasesUpdatedListener. but there are cases where your app is made aware of calling BillingClient.queryPurchasesAsync() as described in Fetching purchases.

Your app should process a purchase in the following way:

1. Verify the purchase.
2. Give content to the user, and acknowledge delivery of the content. Optionally, mark the item as consumed so that the user can buy the item again.

To verify a purchase, first check that the purchase state is PURCHASED. If the purchase is PENDING, then you should process the purchase as described in Handling pending transactions. For purchases received from onPurchasesUpdated() or queryPurchasesAsync, you should further verify the purchase to ensure legitimacy before your app grants entitlement. To learn how to properly verify a purchase, see Verify purchases before granting entitlements.

Once you've verified the purchase, your app is ready to grant entitlement to the user. After granting entitlement, your app must then acknowledge the purchase. This acknowledgement communicates to Google Play that you have granted entitlement for the purchase.

The process to grant entitlement and acknowledge the purchase depends on whether the purchase is a non-consumable, a consumable, or a subscription.

For consumables, the consumeAsync() method fulfills the acknowledgement requirement and indicates that your app has granted entitlement to the user. This method also enables your app to make the one-time product available for purchase again.

To indicate that a one-time product has been consumed, call consumeAsync() and include the purchase token that Google Play should make available for repurchase. You must also pass an object that implements the ConsumeResponseListener interface. This object handles the result of the consumption operation. You can override the onConsumeResponse() method, which the Google Play Billing Library calls when the operation is complete.

The following example illustrates consuming a product using the associated purchase token:

suspend fun handlePurchase(purchase: Purchase) {
    // Purchase retrieved from BillingClient#queryPurchasesAsync or your PurchasesUpdatedListener.
    val purchase : Purchase = ...;

    // Verify the purchase.
    // Ensure entitlement was not already granted for this purchaseToken.
    // Grant entitlement to the user.

    val consumeParams =
        ConsumeParams.newBuilder()
            .setPurchaseToken(purchase.getPurchaseToken())
            .build()
    val consumeResult = withContext(Dispatchers.IO) {
        client.consumePurchase(consumeParams)
    }
}

void handlePurchase(Purchase purchase) {
    // Purchase retrieved from BillingClient#queryPurchasesAsync or your PurchasesUpdatedListener.
    Purchase purchase = ...;

    // Verify the purchase.
    // Ensure entitlement was not already granted for this purchaseToken.
    // Grant entitlement to the user.

    ConsumeParams consumeParams =
        ConsumeParams.newBuilder()
            .setPurchaseToken(purchase.getPurchaseToken())
            .build();

    ConsumeResponseListener listener = new ConsumeResponseListener() {
        @Override
        public void onConsumeResponse(BillingResult billingResult, String purchaseToken) {
            if (billingResult.getResponseCode() == BillingResponseCode.OK) {
                // Handle the success of the consume operation.
            }
        }
    };

    billingClient.consumeAsync(consumeParams, listener);
}

To acknowledge non-consumable purchases, use either BillingClient.acknowledgePurchase() from the Billing Library or Product.Purchases.Acknowledge from the Google Play Developer API. Before acknowledging a purchase, your app should check whether it was already acknowledged by using the isAcknowledged() method in the Google Play Billing Library or the acknowledgementState field in the Google Developer API.

The following example shows how to acknowledge a purchase using the Google Play Billing Library:

val client: BillingClient = ...
val acknowledgePurchaseResponseListener: AcknowledgePurchaseResponseListener = ...

suspend fun handlePurchase() {
    if (purchase.purchaseState === PurchaseState.PURCHASED) {
        if (!purchase.isAcknowledged) {
            val acknowledgePurchaseParams = AcknowledgePurchaseParams.newBuilder()
                    .setPurchaseToken(purchase.purchaseToken)
            val ackPurchaseResult = withContext(Dispatchers.IO) {
               client.acknowledgePurchase(acknowledgePurchaseParams.build())
            }
        }
     }
}

BillingClient client = ...
AcknowledgePurchaseResponseListener acknowledgePurchaseResponseListener = ...

void handlePurchase(Purchase purchase) {
    if (purchase.getPurchaseState() == PurchaseState.PURCHASED) {
        if (!purchase.isAcknowledged()) {
            AcknowledgePurchaseParams acknowledgePurchaseParams =
                AcknowledgePurchaseParams.newBuilder()
                    .setPurchaseToken(purchase.getPurchaseToken())
                    .build();
            client.acknowledgePurchase(acknowledgePurchaseParams, acknowledgePurchaseResponseListener);
        }
    }
}

Subscriptions are handled similarly to non-consumables. You can acknowledge a subscription Acknowledgement using either BillingClient.acknowledgePurchase() from the Google Play Billing Library or Purchases.Subscriptions.Acknowledge from the Google Play Developer API. All initial subscription purchases need to be acknowledged. Subscription renewals do not need to be acknowledged. For more information on when subscriptions need to be acknowledged, see the Sell subscriptions topic.

Fetching purchases

Listening to purchase updates using a PurchasesUpdatedListener is not sufficient to ensure your app processes all purchases. It's possible that your app might not be aware of all the purchases a user has made. Here are some scenarios where your app could lose track or be unaware of purchases:

• Network Issues during the purchase: A user makes a successful purchase and receives confirmation from Google, but their device loses network connectivity before their device receives notification of the purchase through the PurchasesUpdatedListener.
• Multiple devices: A user buys an item on one device and then expects to see the item when they switch devices.
• Handling purchases made outside your app: Some purchases, such as promotion redemptions, can be made outside of your app.

To handle these situations, be sure that your app calls BillingClient.queryPurchasesAsync() in your onResume() and onCreate() methods to ensure that all purchases are successfully processed as described in processing purchases.

Handling purchases made outside your app

Some purchases, such as promotion redemptions, can happen outside of your app. When a user makes a purchase outside of your app, they expect your app to show an in-app message, or use some kind of notification mechanism to let the user know that the app correctly received and processed the purchase. Some acceptable mechanisms are:

• Show an in-app popup.
• Deliver the message to an in-app message box, and clearly stating that there is a new message in the in-app message box.
• Use an OS notification message.

Keep in mind that it is possible for your app to be in any state when your app recognizes the purchase. It is even possible for your app to not even be installed when the purchase was made. Users expect to receive their purchase when they resume the app, regardless of the state in which the app is.

You must detect purchases regardless of the state in which the app is when the purchase was made. However, there are some exceptions where it may be acceptable to not immediately notify the user that the item was received. For example:

• During the action part of a game, where showing a message may distract the user. In this case, you must notify the user after the action part is over.
• During cutscenes, where showing a message may distract the user. In this case, you must notify the user after the cutscene is over.
• During the initial tutorial and user setup parts of the game. We recommend you notify new users of the reward immediately after they open the game or during initial user set up. However, it is acceptable to wait until the main game sequence is available to notify the user.

Always keep the user in mind when deciding when and how to notify your users of purchases made outside of your app. Any time a user doesn’t immediately receive a notification, they may get confused, and may stop using your app, contact user support, or complain about it on social media.

Handling pending transactions

Google Play supports pending transactions, or transactions that require one or more additional steps between when a user initiates a purchase and when the payment method for the purchase is processed. Your app should not grant entitlement to these types of purchases until Google notifies you that the user's payment method was successfully charged.

For example, a user can create a PENDING purchase of an in-app item by choosing cash as their form of payment. The user can then choose a physical store where they will complete the transaction and receive a code through both notification and email. When the user arrives at the physical store, they can redeem the code with the cashier and pay with cash. Google then notifies both you and the user that cash has been received. Your app can then grant entitlement to the user.

Your app must support pending transactions by calling enablePendingPurchases() as part of initializing your app.

When your app receives a new purchase, either through your PurchasesUpdatedListener or as a result of calling queryPurchasesAsync(), use the getPurchaseState() method to determine whether the purchase state is PURCHASED or PENDING. Note that you should grant entitlement only when the state is PURCHASED. If your app is running when the user completes the purchase, your PurchasesUpdatedListener is called again, and the PurchaseState is now PURCHASED. At this point, your app can process the purchase using the standard method for processing one-time purchases. Your app should also call queryPurchasesAsync() in your app's onResume() and onCreate() methods to handle purchases that have transitioned to the PURCHASED state while your app was not running.

Your app can also use Real-time Developer Notifications with pending purchases by listening for OneTimeProductNotifications. When the purchase transitions from PENDING to PURCHASED, your app receives a ONE_TIME_PRODUCT_PURCHASED notification. If the purchase is cancelled, your app receives a ONE_TIME_PRODUCT_CANCELED notification. This can happen if your customer does not complete payment in the required timeframe. When receiving these notifications, you can use the Google Play Developer API, which includes a PENDING state for Purchases.products.

Handling Multi-quantity purchases

Supported in versions 4.0 and higher of the Google Play Billing Library, Google Play allows customers to purchase more than one of the same in-app product in one transaction by specifying a quantity from the purchase cart. Your app is expected to handle multi-quantity purchases and grant entitlement based on the specified purchase quantity.

To honor multi-quantity purchases, your app's provisioning logic needs to check for an item quantity. You can access a quantity field from one of the following APIs:

• getQuantity() from the Play Billing Library.
• Purchases.products.quantity from the Google Play Developer API.

Once you've added logic to handle multi-quantity purchases, you then need to enable the multi-quantity feature for the corresponding product on the in-app product management page in the Google Play Developer Console.