I know, was actually a typo in the callback URL.
Putting this on hold for the time-being. It’s stuck now with “invalid gateway” (or similar) and an error about “JWKS_NOT_FOUND” and there are no usable logs on the other end.
The URLs are configured correctly, as far as I can tell. And are reachable.
If anyone else has ideas and/or wants to look into this further, please let me know and I can help with testing in that case.