Android Bookmarks - Sync error


I would like to use the “Nextcloud Bookmarks” app from Apps Emasty on my Android smartphone. I can connect to my server via the app and also log in. When I start the synchronisation process, the following error message appears:

I am already in contact with the developer. However, they have not been able to help me yet. Does anyone know this error message or have an explanation for it?
I also sync my bookmarks with Floccus in Firefox and Edge, which works fine.

Nextcloud 20.0.12
NextCloudPi Version 1.41.10 (RaspberryPi 3B+)
Android Bookmarks Version 0.3.4

Kind regards,

Which version of the bookmarks app is installed on your server? It would be helpful to know which API endpoint is causing trouble.

Hello Marcel,

installed version on the server is 10.0.2.