GET - https://subscribercrmapi.oss.org.uk/api/payment/{id}
Get an individual Payment.
{ "Id": 1, "ContactId": 1234, "DemandId": 567, "Amount": 50.0, "TransactionDate": "2026-05-22T00:00:00+00:00", "Comments": "ABC123", "PaymentMethodId": 1}