Can you try this in your web.config file.
Under your system.webserver settings check if you have this enabled.
P.S:- You need to keep those two settings to blank or if you want to support you could do like this
Friendly URL extension - `.aspx;.html;.htm;;
Files friendly URL extension - Keep it blank, this will ensure no extension being added to your file and they will be accessible as it is`
Let me know if this works.