Getting Error While testing Google In-App purchase Subscriptions

I am implementing google In-app purchase subscriptions in Android app for testing product of id android.test.purchased but getting following error.

{ "code": -e, "message": "could not complete purchase", "text": "Signature verification failed for sku android.test.purchase(response: -1003:Purchase signature verification failed)", "response": -1003, "errorCode": -6 }

I have uploaded app in internal testing of Google play console and downloaded app from there. I have added all required permissions but still getting this error. Any help would be appreciable. Thanks in advance.