Can't run the security scan on my Nextcloud

Hey, I’m trying to run the security scan on my freshly registered Nextcloud.

The address of my Nextcloud is:

If I enter the URL in the security scan line, I got the error message:

“Scan failed! The scan for the specified domain failed. Either no Nextcloud or ownCloud can be found there or you tried to scan too many servers.”

What do I have to do in order to check if my Server / Nextcloud installation is secure?

known problem: Nextcloud Security Scan: Scan failed!
unfortunately it’s not sure when it will be fixed.