So I have for now a simple php file that looks like that:

<?php

header('Access-Control-Allow-Origin: *');
header('Access-Control-Allow-Methods: GET, POST, DELETE, OPTIONS, PUT');
header("Access-Control-Allow-Headers: *");
echo 'test';

And I’m trying to call it from a SvelteKit form just like that:

<form
    action="http://the.ip.adress:16000/add"
    method="post"
    enctype="multipart/form-data"
    use:enhance={() => {
        return async ({ result }) => {
            console.log(result);
            if (result.type === 'success') {
                alert('Fichier ajoutée avec succès');
            }
        };
    }}
>
</form>

I am calling it from localhost to a specific IP adress, but everytime I call it, it returns this error:
Access to fetch at 'http://the.ip.adress:16000/add' from origin 'http://localhost:5173' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled

And when I check the network tab, it sends two request, one fail and doesn’t returns headers and the other succeed with the headers returned.