Reply To: Cannot retrieve field value in PHP custom plugin

Good morning, I’ll try to explain:
I‘m passing a parameter via shortcode to a hidden field
Then I want to use that field value to populate some other hidden fields. To populate those fields I have to pick data from an external database with a sql query, so I was trying to do it with a custom php plugin. This is the code:

if ($mysqli->connect_errno) {
    printf("Connessione al db fallita: %s\n", $mysqli->connect_error);
    exit();
}

$query = "SELECT nome, sessione, anno, prezzo, paypal FROM corsi_new WHERE id_iscrizione='".$corso."'";

$result = $mysqli->query($query);

$row = $result->fetch_row();

$corsoid=$row[0]."-".$row[1]."-".$row[2];

add_filter('quform_element_value_Titolo-corso', function ($value) use ($row) {
    	return $row[0];
});
 
add_filter('quform_element_value_Sessione', function ($value) use ($row) {
    	return $row[1];
});
 

add_filter('quform_element_value_Anno', function ($value) use ($row) {
    	return $row[2];
});

add_filter('quform_element_value_CorsoID', function ($value) use ($row) {
    	return $corsoid;
});
 

add_filter('quform_element_value_Prezzo', function ($value) use ($row) {
    	return $row[3];
});
 

add_filter('quform_element_value_Paypal', function ($value) use ($row) {
    	return $row[4];
});