Can't use app data after upgrade to NC 13.0.0

The error 998 says that the object was not found:
https://docs.nextcloud.com/server/13/developer_manual/core/externalapi.html

Are you sure the app is installed? Can you reproduce this test with the demo instances

?

In this case, it’s probably the best to report it directly to the developers on Issues · nextcloud/server · GitHub. Normally owncloud and Nextcloud were close enough that this library should work on both.