Hello EA team, I'm having trouble trying to redeem codes for FC Mobile.

Hi there! Welcome to our forums.
It sounds like you may be logging into the web redemption portal using a different email account than the one associated with your active in-game profile. Even if both accounts use similar addresses or are connected via Facebook, the web portal requires you to log in with the exact EA Account email linked inside your game settings to find your player data. Please double-check your in-game account settings for the exact email, try logging in again, and let me know if that resolves the error!