Good evening Ulli and welcome back!
Thank you for reaching out to us.
I would love to help you with this topic.
Based on the information I have, it looks like you have a personal license.
This is why you are being limited to 1 site.
The good news is that it is possible to move that license around, should you need to:
- https://theeventscalendar.com/knowledgebase/license-key-out-of-installs/
- https://theeventscalendar.com/knowledgebase/moving-your-license-keys/
Alternatively, you could also upgrade to a business license or more, should you need a license for multiple sites: https://theeventscalendar.com/knowledgebase/upgrading-a-license/
Let me know if that helps.
Have a great day!
Geoff B.