AS2 MDN Error

I am setting up as2 connectivity to a partner. I can send them data but when the MDN comes back it shows this error “MDN Disposition: automatic-action/MDN-sent-automatically; processed/error: unknown-trading-relationship”

I have verified all certs on their side and mine. The partner says they are sending a signed MDN. I dont know why it is failing.
I did notice that partners MDNs that are working have a content type of multipart/signed where the MDN from this partner is multipart/report. They dont know where that is being set.

Any ideas?

The error:
processed/error: unknown-trading-relationship
is generated by the client system.
You should ask them to check if they enabled the relationship between the AS2 From ID and AS2 To ID in their application.

I agree with Tong Wang on this.