If your contract was issued under a GSA schedule, then your GSA Contract Number entry needs to be accomplished by using the Reference Procurement Identifier field located on the Pay DoDAAC page as shown in the image below. Entering a Reference Procurement Identifier is always optional, but may be used any time the order has been placed under a parent agreement, such as a GSA schedule.

The user enters the "Reference Procurement Identifier" from their contract if not pre-populated from EDA.