Our requirement is a Connector. We need to connect with a multipart/mixed REST API which accepts json request as well as a file. Our requirement is to update only the json part and we would not send any file in the request. We formed the json request in the body and not getting any success. Any mandatory properties that need to be set while integrating with this kind of multipart APIs. I gave the header as multipart/mixed; boundary=---Content Boundary(as given by the API team) in the Content-Type header in the connector rule.
We don't support multipart/mixed OOTB. We only support multipart/form-data via the use of pyRequestAttachmentPage. You can still use REST connector to construct such a request. These are the changes you need to make: