All code for Validating Android In-App Purchases With Laravel blog post: http://blog.goforyt.com/validating-android-app-purchases-laravel/

androidPurchaseReceipt.json

{
    "receipt": {
        "type": "android-playstore",
        "id": "12345678901234567890.1234567890123456",
        "purchaseToken": "purchase token goes here",
        "receipt": "{"orderId":"12345678901234567890.1234567890123456","packageName":"com.example.app","productId":"com.example.app.product","purchaseTime":1417113074914,"purchaseState":0,"purchaseToken":"purchase token goes here"}",
        "signature": "signature data goes here"
    }
}

makeGoogleRequest.php

<?php

try {
    // create new Google Client
    $client = new Google_Client();
    // set Application Name to the name of the mobile app
    $client->setApplicationName("Mobile_App_Name");
    // get p12 key file
    $key = file_get_contents($_ENV['GOOGLE_KEY_PATH']);
    // create assertion credentials class and pass in:
    // - service account email address
    // - query scope as an array (which APIs the call will access)
    // - the contents of the key file
    $cred = new Google_Auth_AssertionCredentials(
        'Service Account Email Address',
        ['https://www.googleapis.com/auth/androidpublisher'],
        $key
    );
    // add the credentials to the client
    $client->setAssertionCredentials($cred);
 
    // create a new Android Publisher service class
    $service = new Google_Service_AndroidPublisher($client);
 
    // set the package name and subscription id
    $packageName = "com.example.app";
    $subscriptionId = "com.example.app.subscription";
 
    // use the purchase token to make a call to Google to get the subscription info
    $subscription = $service->purchases_subscriptions->get($packageName, $subscriptionId, $purchaseToken);
} catch (Google_Auth_Exception $e) {
    // if the call to Google fails, throw an exception
    throw new Exception('Error validating transaction', 500);
}

storePurchaseReceipt.php

<?php

$rawReceipt = $command->getReceipt();
$receipt = json_decode($rawReceipt['receipt'], TRUE);
 
if (isset($receipt['purchaseToken'])) {
    $this->transactionRepo->addReceiptBeforeValidation($user->id, $platform, $receipt['purchaseToken']);
} else {
    throw new ValidationException('No receipt data found', 250);
}

subscriptionError.json

{
    "error": {
        "errors": [
            {
                "domain": "global",
                "reason": "invalid",
                "message": "Invalid Value"
            }
        ],
        "code": 400,
        "message": "Invalid Value"
    }
}

subscriptionValid.json

{
    "kind": "androidpublisher#subscriptionPurchase",
    "startTimeMillis": long,
    "expiryTimeMillis": long,
    "autoRenewing": boolean
}

validateResponse.php

<?php

if (is_null($subscription)) {
    // query returned no data
    throw new ServerErrorException('Error validating transaction.', 500);
} elseif (isset($subscription['error']['code'])) {
    // query returned an error
    throw new ServerErrorException('Error validating transaction.', 500);
} elseif (!isset($subscription['expiryTimeMillis'])) {
    // query did not return a subscription expiration time
    throw new ServerErrorException('Error validating transaction.', 500);
}
 
// convert expiration time milliseconds since Epoch to seconds since Epoch
$seconds = $subscription['expiryTimeMillis'] / 1000;
// format seconds as a datetime string and create a new UTC Carbon time object from the string
$date = date("d-m-Y H:i:s", $seconds);
$datetime = new Carbon($date);
 
// check if the expiration date is in the past
if (Carbon::now()->gt($datetime)) {
    throw new ServerErrorException('Error validating transaction.', 500);
}