Can't fetch an api on Vercel backend cause of Content-Security-Policy

I’m trying to get the Twitch user Username when the Extension starts but when I fetch to my backend (hosted on Vercel) it returns an error because the Content-Security-Policy doesn’t allow it.

How can I communicate with my backend avoiding this error?

Did you add your backend to the allowlist (fetch domains) in the developer console?

yeah I did that and now it works.
Didn’t kwon about that

See also the relevant documentation: Life Cycle Management | Twitch Developers and Extensions | Twitch Developers