SAP Message WTADDI255 - Please enter a reference purchase order number for additionals

Diagnosis
To request an additionals IDoc you must specify the purchase ordernumber of the relevant purchasing document.
A purchase order was generated for the additional. The input parametersmust include the purchasing document number (AddiBuyHeadID) andthe item (AddiBuyItemNo).

System Response
No additionals IDoc is generated.

Procedure
Check the parameters.