Hello, I'm having a issue with requesting the access token and refresh token from the https://api.amazon.com/auth/O2/token given that I successfully generated a auth code.
I followed the tutorial to login with amazon in an iOS: https://developer.amazon.com/docs/dash/lwa-mobile-sdk-ios.html
I created a code challenge and used S256 as the code challenge method.
My idea is to convert the auth code to a access/refresh token using my backend, once I trigger the API call https://api.amazon.com/auth/O2/token providing everything including the code challenge I'm getting the error "unauthorized_client", if I do the same thing using "plain" as the code challenge method I can successfully retrieve the access/refresh tokens, is there a reason for this? Can someone help me troubleshoot?