Change format from index.html to index.php but got HTTP 500 error

[Oxy]

and that path for includes is also silly

Http error 500

When trying to access your website, you may see a page which returns the status code “500”. In Google Chrome, you’ll see a page with the error code HTTP ERROR 500. There are typically two reasons which can cause this error: The PHP code has crashed. The .htaccess file contains invalid rules. Here are some things you can try to debug and fix this. Fixing crashing PHP code A HTTP ERROR 500 simply tells you that the PHP code has crashed, but gives no information as to why it has crashed. Gett…

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Can you tell us briefly what you actually want to achieve?
What is the purpose of all this?

I have a feeling that maybe you could solve it with .htaccess