POSTing to /customers/{id}/beneficial-owners in the Dwolla sandbox with a complete, correct-looking body (firstName, lastName, ssn, dateOfBirth, address) returned {"code":"NotFound","message":"The requested resource was not found."} instead of 201 — even via Dwolla's official Postman collection. A Dwolla maintainer checked the logs: the customer was a 'Receive Only' customer type, which isn't eligible to add beneficial owners. The fix on the user side is to run beneficial owner operations against a Business Verified Customer, since Receive Only customers are not eligible.