When the Redirect URI doesn’t match one of the redirect URI’s listed in the console.
Twitch will redirect to the first listed redirect URI in the console with that error.
This suggests that you specified an invalid/unmatched redirect URI in your outbound link to Twitch.
Commonly this can be a missing / on the end of the URI in the console or not URI Encoding the redirect URI in the outbound link.
So without a copy of how you are constrcuting your outbound link and a screenshot for your console I can’t tell you what specifically is wrong