Collabora doesn't work - ERROR "Try again later"

made a fresh installation (Ubuntu Focal) and Nextcloud 22.1.1. Everything is working - just Collabora doesnt work. If I try to open / create a document, it takes some seconds and I get the error “Cant reach Collabora online - try again later”. But NC says “Collabora Online Server is reachable”.

In the logfiles I found the following error:

Error richdocuments Exception: Could not find urlsrc in WOPI

I searched a lot in Google. Seems that many have had this error. But found nothing wich helped. Please, is there anybody out there who had the same error and a solution?

NC: 22.1.1
Collabora Online: 4.2.3
Collabora Online - Built-in CODE Server: 6.4.1004

Thanks a lot for any help!

Cheers Walhalla