This is a payment method emulation, so it works in a rather specific way:

init

Since this is a test payment method, no redirection is required, and there will be no redirection data in the response.

The transaction status is changed from I (STATUS_INITIALIZED) to P (STATUS_INPROGRESS)

PATCH api/storefront/carts/{cart-id}/payment/{public-txn-id}

{
  "action": "init"
}

pay

It is possible to specify the required result in the code field

S - Completed P - Pending F - Failed

PATCH api/storefront/payment/{cart-id}/payment/{public-txn-id}

{
  "action": "pay",
  "actionData": [
      {
          "name": "code",
          "value": "S"
      }
  ]
}