“An error occurred whilst communicating with the server” or “Error connecting to the server” Moodle 3.7

I am getting “An error occurred whilst communicating with the server” or “Error connecting to the server” on a Moodle 3.7 site when I try to upload audio or video files. May be becuase the error shows up in a pop up message no debug messages are displayed even though i enabled it in the settings. Strange thing is previously i was able to upload without such errors.

Action taken so far to relove the issue;
increasing following values in php.ini

memory_limit
upload_max_filesize 
post_max_size 
max_input_time 

increasing uploadReadAheadSize, appConcurrentRequestLimit in IIS

I can see the following error in network tab of the browsers inspector
repository/repository_ajax.php?action=upload [HTTP/1.1 413 Request Entity Too Large 448ms]
or
course/dndupload.php [HTTP/1.1 413 Request Entity Too Large 455ms]
I am only trying to upload an audio in 50M size. Uploading word or PDFs produce no errors. I’m trying to resolve this since yesterday. Any help is greatly appriciated!