400 Bad Request - Unknown Payment Method

Indicates the payment method is unknown to SumUp.

{
  "type": "https://developer.sumup.com/docs/problem/unknown-payment-method/",
  "title": "Bad Request",
  "status": 400,
  "detail": "Unknown payment method: NonExistingPaymentMethod",
  "instance": "7fe5fcddbf28"
}