Javier, I’ve tried a million different things, since I last posted. The main things that worked (I think, because I also think the Youtube Module I was using is broken)..
- Changing the Audience (Google Cloud Project / Google Auth Platform/Audience) to External & Testing, then added my email address (the account owner) in the Test Users. When I authenticated in in Make.com - it gave me a warning to tell me the app wasn’t verified, but I could continue past that anyway.
- Adding a MILLION URI’s - see this post - Google Docs Error 400: redirect_uri_mismatch - #7 by samliew
- And then I also changed the Module I was suing - instead of using the create a playlist, I tried upload a video and then I was able to authenticate. I just went back to the old module, and used the connection I had created in the other module, and it worked (As in, I logged in as me, and then it listed the different channels under my account). So it just might be the module.
It was painful - good luck!