An internal server error on a website that you're hosting on PythonAnywhere is an indication that something is going wrong in your code. To find out exactly what that is, you need to take a look at your website's error log. There's a link to the error log on the "Web" page inside PythonAnywhere, and the most recent error message will be at the bottom of the file.
Hopefully once you've seen the message there, you'll be able to debug the problem. If you get completely stuck, then you can contact PythonAnywhere support on email@example.com -- we can help on PythonAnywhere-specific issues, and while we can't in general give programming coaching or tuition, we may be able to point you in the right direction to get help.