See: nextcloud/server#1861
Basically when setting up a new account in the app it connects to /index.php/ocs/cloud/user?format=json
This might have worked for dark hackery reasons in the past. But this is not the valid OCS endpoint.
It should be ``/ocs/v2.php/cloud/user?format=json(note that you need to send theOCS-APIREQUEST: true` header.
Basically this does no longer work in NC11 because we moved OCS to the appframework.