Suse 15 Repository not working

[sdkun3456]

Hello,
I want to run this two commands:
zypper addrepo https://repo.linuxfabrik.ch/monitoring-plugins/sle/linuxfabrik-monitoring-plugins-release.repo
zypper install linuxfabrik-monitoring-plugins

The Repo will be added, but it seems not to be a valid Suse Repository. This happens after runnig "zypper ref":
Retrieving repository 'Linuxfabrik Monitoring Plugins (release)' metadata .........................[error]
Repository 'Linuxfabrik Monitoring Plugins (release)' is invalid.
[linuxfabrik-monitoring-plugins-release|https://repo.linuxfabrik.ch/monitoring-plugins/sle/15/release/] Failed to retrieve new repository metadata.
History:

• [linuxfabrik-monitoring-plugins-release|https://repo.linuxfabrik.ch/monitoring-plugins/sle/15/release/] Repository type can't be determined.
  Please check if the URIs defined for this repository are pointing to a valid repository.
  Skipping repository 'Linuxfabrik Monitoring Plugins (release)' because of the above error.

Best Regards
Steffen