Put the temporary debug code after the code for constructing SQL:
if ($has_data == true)
{
$sql = "UPDATE db_purchase_form SET ";
$sql .= "db_product_name = '" . $product_name . "', ";
$sql .= "db_actor = '" . $choice_actor . "', ";
$sql .= "db_user_name = '" . $user_name . "', ";
$sql .= "db_user_email = '" . $user_email . "', ";
$sql .= "db_vdo_script = '" . $vdo_script . "', ";
$sql .= "db_hrt_msg = '" . $hrt_msg . "', ";
$sql .= "db_port_approval = '" . $portApproval . "', ";
$sql .= "db_delivery = '" . $delivery . "', ";
$sql .= "db_price = '" . $net_price . "', ";
$sql .= "db_date_time = NOW() ";
$sql .= "WHERE id = '{$id}'";
// temporary debug code
die($sql);
}
When you submit the form it should display the SQL and stop the script. Post the output here.