<?php include "config.php"; ?>
<?php

// Connect to database
$query = mysqli_query($con,"SELECT * FROM reservations WHERE reserved='yes' AND confirmed='no'");
$row = mysqli_fetch_array($query);

// set reservation time
$datetime = $row['datetime'];
$datetime -> modify('+3 days');

$now = date("Y-m-d H:i:s");

foreach $query as $row {
   if ($datetime > $now) {
        //it still has time. sent reminder if less than 24 hours left.
   } else {
       //time has passed, set registration inactive.
   }
}
?>