Registration and password reset do not work
The URL should be https://frag.jetzt/...
I asked for a registration and got a password reset:
In addition, the wording of the emails is not user friendly: What if someone misused your mail address?
See: https://postmarkapp.com/blog/password-reset-templates-best-practices or https://www.digitaldesignjournal.com/best-password-reset-request-email-template/