Spotify : 403 - User not registered in the Developer Dashboard

[Alexandra33278]

I'm making a react-native app with the Spotify API, I'm using the Authorization Code Flow & and I'm on Development mode with only one user added in "Users and access" on my Spotify dashboard: my tester, who is a part of my Spotify Premium Duo.

The app is working fine on my part, but my tester can't see anything related to her account. The /me endpoint is sending a 403 error with this message in the body: User not registered in the Developer Dashboard. Top Tracks / Top Artists endpoints are working fine with her Access Token.

I can't see any email on her Spotify account, but can't change anything because it is linked to her Facebook account. I'm also logged in with my Facebook but it's working fine, and I can see my details when fetching the /me endpoint with my access token.

If you ever stumbled upon this kind of error, any help will be appreciated! Thank you in advance.