Hi Moritz,
Check the below notes
- 1952406 No Service configured for key
- 1872390 Handling invalid XML characters
- 1938302 java.lang.NullPointerException: Name is null
The below blog may resolve your issue.
PI 7.3 Java Stack - iDoc AAE not processed - ID... | SCN
Sending and receiving IDOCs using a single stack SAP PO system
Regards
Bhargava Krishna