Diagnosis
Settings have been made in the input parameters for customer/sold-toparty (transaction OVD7) that specify which number should be used as themain reference when transfers to open items of the FI module are made.
However, this information was not available in the respective IDoc.

Procedure
Using the function , you can enter the category and numberfor the main reference.
The error is removed by restarting the verification step. If no furthererrors exist, the IDoc can be processed in the processing step.
The main reference is then transferred to the processing document(s),and used for assignment when incoming payments are posted.