This field contains the American Express-assigned Service Establishment (SE) Number that is used to identify and pay merchants and authorized processors. It is also informally referred to as the “Partner ID” field, because it identifies an organizational “Partner” that has entered into an agreement with American Express to provide services to Cardholders. An invalid entry in this field will result in file rejection.
If you process transactions for multiple merchants, stores or locations, create a separate batch for each entity and enter the SE Number/Partner ID (that corresponds to the records that comprise this batch) in this field.