Post files to backend as a Passthrough via Apigee API Proxy

[SanSamUser07]

I am trying  to send 2 files to the backend as multipart/form-data using POST.But I am getting below error from the backend :

"Missing Parameter: Failed to parse multipart servlet request; nested exception is org.apache.commons.fileupload.FileUploadException: the request was rejected because no multipart boundary was found"

I have enabled streaming on the Proxyendpoint and Targetendpoint but still the same issue.Any pointers ?I have tried with Content-Type as multipart/form-data  and also as multipart/form-data;boundary=<calculated when request is sent>