In your trunk settings, set From User to the same value that you have in Username.
Set From Domain to fpbx.de. If it doesn’t work, try placetel.de.
If you still have trouble, at the Asterisk command prompt type
pjsip set logger on
make a failing call, paste the Asterisk log for the call (which will now include a SIP trace) at pastebin.freepbx.org and post the link here.
Also, please post a copy of your working chan_sip settings.