Collabora on IONOS managed server

Hi there,

I come from installing Nextcloud 21 including Collabora on a managed server, run by IONOS.
Everything works out beautifully, NC runs, settings indicate Collabora Server is available, setting is set to “use CODE”…

But: it won’t work!
Trying to open a document gives an error

I already uploaden an PHP.ini with a memory size of 512M in the root directory of NC - nothing changed.

What can I do?

Thanks so much for help,