Error when trying to connect (Bad healthcheck status)

I’m new to NextCloud and server hosing. I want to get OnlyOffice integrated to my server.

When I add my server address to the OnlyOffice in the admin section. I get the error “Error when trying to connect (Bad healthcheck status)”

I’ve tried following the docker way, but I cannot get that work either.

My server provider: https://myserver.your-storageshare.de/ (if this helps)