Connection Timed out

We are sending multipart form data through kong to an upstream server. The response is upstream timed out.

Error is as follows -
upstream timed out (110: Connection timed out) while reading response header from upstream.

The same things works fine if the request has ending boundary and new line when checked using postman.

We don’t have control over the web server that is sending this request. So, cant add boundary and new line to the request before it is send to kong.