Extension Bootstrap File Listing - problem

[Seymouria]

Hello.

I have a problem using the Bootstrap File Listing extension.
The directory and target files are on the server.
Unfortunately, after implementing the extension and publishing the page, the effect is as shown in the attached picture.

Image: https://ibb.co/88zkCQh

Example web page with the problem: http://seymouria.pl/0ver.html

This effect is always the same no matter what folder and what file extension I refer to.

I'm asking for advice where to look for the problem ..?
Could this be my hosting problem?

Thanks.

[Pablo]

The extension of the page should be set to 'php'.

[Seymouria]

Of course, now everything works
Thank you so much for helping Pablo.

[WWBman]

Don't forget to delete the .html version (0ver.html).

[Seymouria]

OK, I will remember that.
Thank you for the advice WWBman