Party field empty, no ID mapping for integration

Hello experts,

I have encountered a problem while integrating ECC with C4C using PI. The Sales Orders are arriving into C4C via PI but since the Party field lacks value - I believe that no ID Mapping for integration is picked up and all messages end up with application error since the Customer IDs cannot be mapped (see below):

I have checked the Payload and LocalSystemId is present in it.

Do you know what might be the reason of the Party field being empty?

I have tried to re-activate the Communication Arrangement but to no success.

Any feedback is very welcome.

Kind regards,

Ilja.