Hello, as far as I can see you receive the error message in outbound processing of the IDOC.
We use this scenario for several different messages in different applications.
We do use transmission medium '6' (EDI) in the output type with the EDI_PROCESSING form routine.
But as partner in the partner agreement and also in the output master data a logical system (the logical system for the SAP client) is used.
You could first test by creating an output message manual in your delivery with partner role LS and logical system.
Best regards Jack