Source chains
Settlement is what you configure per flow, so a payer on one chain can pay a merchant settling on another. An exchange payment requires a settlement token and network that the exchange supports, as described in Payment sources.
Testnets
Base Sepolia is the supported testnet. Use these values when you create a test flow and when the payer attaches a source and requests a quote:
Base Sepolia uses
chainName: "EVM". The API guide shows where each field goes.
Next
Settlements
What you receive, on which chain, and where it lands.
Payment sources
The three ways a payer can pay, and which to offer.