Hi Carsten Rieger🔒FOSC (npub1wyf…qzs4), sorry for the late reply.
Configuring UnifiedPush for your Nextcloud involves a few more steps. Kuketz-Blog 🛡 (npub1g6j…4s5g) has published helpful instructions (in German) on how to do that: https://www.kuketz-blog.de/push-benachrichtigungen-fuer-android-via-unifiedpush-nextpush-nextcloud-teil-6/
If you need further support, please open a topic on our forum: https://help.nextcloud.com/
Hope that helped!