Android - In App Purchase - you need to add the BILLING permission to your APK

Have you added this line in your manifest file

<uses-permission android:name="com.android.vending.BILLING" />

You need to add permission to your manifest :

<uses-permission android:name="com.android.vending.BILLING" />

Refer: http://developer.android.com/google/play/billing/billing_integrate.html

Since September, 2017 is not necessary anymore to add <uses-permission android:name="com.android.vending.BILLING" />

Play Billing Library 1.0 Release (2017-09-19, Announcement)

Important changes

Embedded billing permission inside library’s manifest. It's not necessary to add the com.android.vending.BILLING permission inside Android manifest anymore.

https://developer.android.com/google/play/billing/billing_library_releases_notes#release-1_0

Just ensure that you are using the latest version of 'com.android.billingclient:billing' in your app gradle configuration file.