Connect RSpace <-> NextCloud

we have the following problem:
We are using Nextcloud successfully for ~1 year now. Also we started to roll out an elctronic lab book for our scientists. This software (Rspace) has a working integration for OWNCLOUD, but not for Nextcloud. Following the steps (ownCloud Integration - RSpace Help) I can login in nextcloud, but the application shows no files or folder. Just an error
message appears. On the nextcloud I do not see any faults or errors.
Where can I find more information about the problems (enable debug log for oauth as an example), or do i have to use wireshark to look at the communication ?
I have a working test setup (two severs) and would like to take a closer look at the problem…