To add in-app products, you need to add the billing permission to your APK prompt in Google Console In-App Products

Here is the sample prompt:

The issue you are pertaining to wherein you see “To add in-app products, you need to add the billing permission to your APK”, means you have a billing permission issue on your Google Play Console.

I will be adding the steps provided on the previous thread here again to resolve the issue:

1. Create an android release app build. BuddyBoss App > Build. Once done, download the .AAB file.
2. On the Google Play Console, go to Testing > Closed Testing > Create Track > Create a New Release.
3. Upload the .AAB file under the App Bundles section.
4. Click Save then click Review Release.

Now, it is really important you must do a release app. If you upload a test app, you’re gonna get a Test Application ID name in App Bundles which means it is not the one for release which basically puts your entire app to a point of being deleted, you’re gonna have to start all over again. 

You may also check further information on Testing IAP in your Test App vs Release app here: https://www.buddyboss.com/resources/docs/app/in-app-purchases/testing-in-app-purchases/