So I have PHP script running on cron daily. It is suppose to check the date and send an email if it is 7 days before any payments as a reminder. I haven't used PHP in a long time so sorry if the way I did it was ridiculous or something. Thanks a lot. I would say what the problem is but I don't get any error message or anything..

<?php
mysqli_connect("xxxxxx", "xxxxxxx", "xxxxxxxxx") or die(mysqli_error());
mysqli_select_db("xxxxxxxxx") or die(mysqli_error());
//Retrieve original payment dates and enter them into an array
$result = mysqli_query("SELECT DateCreated FROM UserTable");
$payment_dates = mysqli_fetch_array($result);

//Puts original payment date into month-day format
$md_payment_dates = substr($payment_dates, 5);

//Gets todays date in m-d format and adds 7 days to it
$due_date = mktime(0, 0, 0, date("m"), date("d")+7);

//Checks if any payment days match today's date. If there are none it script will stop.
if (count(preg_grep($due_date, $md_payment_dates)) > 0) {
 //Retrieves usernames of users that have an invoice due.
 $users_to_pay = mysqli_fetch_array("SELECT Username IN UserTable WHERE DateCreated = $date");

 //Notifies you via email
 $to = "[email protected]";
 $subject = "7 Day Payment Reminder";
 $message = "Hi, <br /> The following owe a payment in 7 days :  " + $users_to_pay ".<br/> Their payments are due on " + $md_payment_dates " of this year.";

 mail($to, $subject, $message);
 exit();

 }else{
exit();
 }
?>