This document will explain that there is an error in documentation:
* Swagger UI does not support multipart form data.
* Chrome Postman does not support multipart form data.
Will Swagger UI support multipart form data?
Test Data Manager 4.2
The API /TDMModelService/api/ca/v1/objects for registering objects accepts multipart/form-data as the request body.
Each request part (body, files) are of different content-type. Swagger UI does not support providing this kind of request body nor does the Chrome Postman.
There is an another tool, Soap UI which can be used for this.