Problem to sync with WebDav (ionos hidrive)

Hi,
I created syncs on ios and macOS apps successfully - but on https://app.joplincloud.com/ I’m not able to setup the connection to my webdav (https://webdav.hidrive.ionos.com/users/USERNAME/)
If I try to check the connection I always get Error “Failed to fetch”
I have no special settings!

Hope to get a solution

Greetings
Rainer