Several php errors

Hi guys,

tried to integrate OnlyOffice to my Nextcloud but i dont know, how to solve these errors (screenshot below)

If i create a document, i am able to edit the file properly, everythings fine. But as soon, as i share this document with other groups, they end up with a failure (ONLYOFFICE cannot be reached. Please contact admin.)
And this is, what the log then shows.
Certficates are both self signed (For the docker [seperate VM] and Nextcloud)

Any idea?