Sorry to type in English, but I don't speak German (I follow this forum via Google Translate ).

We had the same issue and I guess we have a solution/workaround for this problem. We guess the problem is that the PBX cannot reach the application platform by the external resolved IP-address (and the RP is not (yet) configured).

So to avoid this:

* Don't use an external DNS-server in the install (we used 8.8.8.8 as 'second' DNS-server, if we omit it, the install installs all apps).

* During the install, activate the DNS-servers of the PBX, pointing to the internal IP-addresses (see screenshot below).

Remark: this can also be done while your in the page where the apps are being installed, the install will continue shortly after you added the DNS-entries.

This worked for us (we had the issue for some time) and thanks to Gerrit Beuko we found the workarounds.

P.S. This problem seems to be version-independant.