Missing Android documentation

[znoooo]

Hey, some time ago I've seen the google documentation to verify payments and subscriptions, actually I can't find it anymore.
There is something? Because my integration actually is broken, I can't verify subscriptions.

Actually what I'm doing to verify a subscription is:

$subscription = new Subscription($client, "$packageApp", "$productId", "$purchaseToken");	
$subscription->acknowledge(); // 403 Forbidden
$resource = $subscription->get(); 
$paymentState = $resource->getPaymentState(); 

I got 403 Forbidden from the second line , I'm importing correctly the key and have the account set on play store.

Thank you