IIS 502 – Web server received an invalid response while acting as a gateway or proxy server

Good day all,

i am a newbie in windows server environment forgive me for any technical jargon. I created a php web application in an enterprise environment i.e following the 3 tier architecture(db ,application and web server) . The issue i have is that whenever i upload a large file(100mb) in the web server i get this error :502 – Web server received an invalid response while acting as a gateway or proxy server. The same size uploads successfully on application server. But when the file size is small ,no error is returned. I have increased the file size and execution time both in php.ini and iis. I have been battling this error for over 2weeks.

I need your help urgently . Thanks.