The External Reference ID (<externalRefID>) field, in the simplePayment XML file, identifies the invoice in the external accounting system. This maps to the Reference No. field on the Transaction Data Entry form.
It is important to note that a user will override a previous payment when importing a new payment with the same <externalRefID> on a transaction. As a result unique reference IDs for payments are required.
Payment/receipt is created/posted in an Accounting System
Unique journal ID is populated. (Accounting System's cash transaction ID must be the reference ID sent to VIP)
Note: Adding multiple payments to a transaction is possible when the <externalRefID> is different for each payment. For payments against multiple invoices; each invoice should be added to the <invoiceList> element for a single unique <externalRefID>.
Linking the invoices in multiple messages will not work.