Hello again,
I found a solution:
If anyone runs into the same trouble you should read:
https://community.asterisk.org/t/realtime-pjsip-trouble-failed-to-create-outgoing-session/79914/17
But don`t forget to update odbcinst.ini after changing the driver! - like me ;-))
The link provided by peter doesn`t work anymore. I found the driver at:
https://community.asterisk.org/t/realtime-pjsip-trouble-failed-to-create-outgoing-session/79914/17
Thanks you very much for filling this forum with so many useful informations!
Buschi