WordPress passes the page as GET
but your form uses POST
. The two are different things. POST
data never shows up in the URL like this: /wp-admin/admin.php?page=martial-patientenbeheer.php?naam=naam&vnaam=
It is sent in the headers.
Put var_dump($_POST)
at the top of your callback and you should see your post data. You are looking for the data in the wrong place.