Every market has its own settlement system. We use the local rail instead of pushing everything through SWIFT.
A payment rail is the infrastructure that moves money inside a country: Pix in Brazil, SEPA across the euro area, SPEI in Mexico, ACH and Fedwire in the United States. They are domestic systems, and they are fast and cheap precisely because they never cross a border.
Unbound connects directly to those rails on both legs of every transaction. The result is settlement in minutes or seconds where an international wire would take days, with reconciliation by your own reference instead of manual tracing.