This error was driving me crazy. There were no logs that I could find and the html was just
<h1>Incomplete Response Received from Application</h1>
My localhost was working fine though. The reason was that I was using a library that I had not yet installed! I was using “import requests” but this was not on my “pip3 list”.
The solution was to run “pip3 install requests”. Then restart the server and it worked like magic!