Problem scenario
You know foobar.html is in a directory on a web server that houses index.html. You cannot go to foobar.html in a web browser -- but you can go to index.html. How do you fix this?
Possible solution #1
Are the permissions of foobar.html different from index.html? Is there a slight spelling error in the file name on the back-end? Verify the address in the browser and that it matches up with what is in the back-end.
Possible solution #2
If you are using Flask, then read this possible solution. Is there a route to foobar.html? You may want to view this external page for more information.
Is a function name duplicated in the webapp.py file? (To handle duplicates, see this StackOverflow.com posting.) The route or function governing it may be misconfigured. One problem could be that the templates directory does not actually have the file or there is a small spelling mistake in the file on the back-end.
Is the templates directory configured to be somewhere different for the web page? You may want to view this page: https://stackoverflow.com/questions/31002890/how-to-reference-a-html-template-from-a-different-directory-in-python-flask/31003097