AmountCents is the amount to charge, in whole cents (5000 is $50.00). Server-side bounds apply and are authoritative — the default floor is $1 and the ceiling $5,000, so a fat-fingered or hostile amount is refused before any money moves.
IdempotencyKey makes a retry safe: the same key never charges twice, it replays the first result. Sending one is strongly recommended for an agent, which retries by construction. Empty falls back to a windowed key derived from the amount and currency, so a double-submit inside 15 minutes still collapses onto one charge.
SourceID is the single-use payment token that stands in for the card: a Square Web Payments SDK nonce minted in the browser, or a Square sandbox test nonce when the org's credentials are sandbox ones. The card number itself never reaches this process, which is what keeps it out of PCI scope.
