Drives the same domain command chain a real upstream payment-processor webhook would trigger, so client integrations can exercise inbound-payment flows without a live counterparty. Sandbox-only: the simulator is registered exclusively when the platform runs in Simulated integrations mode, so in Real or Mocked mode this endpoint returns 404 for every request. accountId is the beneficiary account's id, as returned by GET /v1/accounts. amount is expressed in minor units. When remitter is omitted, fixed sandbox defaults are applied (holder name 'Sandbox Remitter Ltd', account number 'SBX0000000001', bank code 'SBXBANK01'). paymentType is one of Fps, Chaps, Swift, Sepa (case-insensitive); Sepa must be in EUR, and any other value is rejected with 400. A reference starting with the documented PAYMENT-rejected-compliance trigger makes screening reject the payment: the id is still returned, but the funds are never allocated to the account.