Interface PaymentMethodCapability

Hard per-method CUSTOMER-country constraint (ISO 3166-1 alpha-2, uppercase) — a rail only customers in specific countries can pay with (Bacs needs a UK bank account, Interac a Canadian one). ABSENT or empty means unrestricted. Screening consults it only when the session states customerCountry; with no country stated the rail passes — a best-effort pre-filter, never an eligibility guarantee, because the true constraint is the bank account the customer brings. Declare only what the provider documents as a country (or a short closed list); a zone rail (SEPA) stays undeclared — encoding the zone's membership would screen out valid payments the day it drifts.

Hard per-method currency constraint (ISO 4217, uppercase) — a rail that settles in one currency only (SEPA in EUR, Bacs in GBP). ABSENT means unrestricted; the PSP-wide AdapterCapabilities.supportedCurrencies still applies on top. Declared rather than guarded privately so the router can pre-screen: a currency-ineligible rail must be skipped in favour of an eligible PSP, not attempted and rejected at the PSP.