In Xero, prepayments record payments made before an invoice is raised or a supplier bill is received. These can be created directly in your bank account, during bank reconciliation, or as a "spend" or "receive money" transaction.
SFX supports prepayments, which function similarly to invoices but involve payments made by customers in advance.
Within Salesforce, you can create a Xero custom object mapping in SFX that mirrors your invoice mapping. You will simply need to set the record type to "Prepayment," as shown in the screenshot below.
See below Pre-payment mapping