How do I connect my Wixsite to PHP?

Well, the title says it all. I have this PHP-code to create a private message system, but I have no idea how I should connect the code to the list of users. Can anyone help me?

Currently, Wix only supports adding HTML code, which can be added through the HTML element. It is not possible to add PHP code to your Wix site.

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In the future, try the Wix Help Centre.