Somehow we managed to get a domain ban for iframe embeds of youtube videos - and find NO WAY to get it lifted!
The error is this:
"debug_error": "{"errorCode":"auth","errorDetail":"0","errorMessage":"Video nicht verfügbar","Ak":"Dieses Video darf nicht auf dieser Domain gezeigt werden","NQ":"0;a6s.0","hB":2}",
The same video embedded on our “sister”-page https://www.formel1.de is working correctly. So, the reason for the error CANNOT be the video itself.
I made some test pages OK: https://www.formel1.de/ytembedtest.html
OK: https://www.ms-total.com/ytembedtest.html
NOT OK: https://www.motorsport-total.com/ytembedtest.html (The source is always identical)
You can lift the ban? Who is to contact?
If you want to verify that your website complies with Youtube's policies, you can do so by requesting a compliance audit here: https://support.google.com/youtube/contact/yt_api_form (Yes, I know that this form seems unrelated, but this form is actually a catch-all for most API-related issues.)
and you can file an actual appeal here: https://support.google.com/youtube/contact/yt_api_appeals
More information: https://developers.google.com/youtube/terms/developer-policies
You might also want to verify that your settings, if you have any, on https://studio.youtube.com/ and the Google Cloud Console are correct, though it seems unlikely to be related.
Good luck!