localhost sends back invalid response using Google callback

[SkepticMystic]

Hi there

I've been trying to add Google OAuth to my project using the sample code provided in the readme and the example app.
I have created appAuth, as well as the needed Google ID and secret.
When logging in, I get correctly redirected to the google account picker page. But after choosing an account, I get this error when being redirected to the callback:

Just to be sure, I have not configured a /api/auth/callback/google route (I assume the api/auth/[...auth].ts route handles it?).

Any help would really be appreciated, thanks :)