Missing multipart field contentAnalyzerRequests

I am always seeing this error when trying to hit the document generation API-

"Missing multipart field contentAnalyzerRequests"

{"requestId":"Klh4nbPHhMLemhRTuBPsaeCvprx6776a","type":"Bad Request.","title":"Missing multipart field contentAnalyzerRequests","status":400,"report":"{\"error_code\":\"INVALID_REQUEST\"}"}