Some testers got 403 error even were added to dev dashboard

[MATCH_Dev]

Plan

Premium

Country

AU

Device

iPhone and Galaxy

Operating System

iOS and Android

My Question or Issue

Hi Spotify team,

I am developing an app integrating web APIs and it is now on beta test. Some testers reported they received 403 error when trying to query endpoints '/me', '/playlist', etc. This issue consistently happens on only part of the testers and I have included all of them in dev dashboard (with 25 head counts). I have test one of problematic account by querying web API with CURL and issued access token (I used PKCE to get token by the way) and got this error message:

Check settings on developer.spotify.com/dashboard, the user may not be registered.

This is weird as I am sure all these user account was included in the dashboard. Do you have any clue on what happened to these accounts (they are all premium users as the rest)?