POST request converted to GET

[Yahiakd]

I have a simple html form using POST request, however when recieving the data on the action file, my POST request doesn't exist.
When i check the request methode using $_SERVER['REQUEST_METHOD'] it returns a 'GET'.
So for some reason my POST gets rewritten as GET (i can also see the data sent in the URL).
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Here is the html form :

And here is the relevant part of the action file (add.php) :

Notice how i'm using '$_GET['submit'] to collect my data, and it actualy works even though i used a POST request. (when i use $_POST['submit'] the isset($_POST['submit'] returns false obviously)

Thank you for your time.