on the BookingRequestDM_Update.php page, the action is to post to another page:
<form action="BookingRequest_Update.php?BookingRequestID=<?php echo(rawurlencode($row_WADABookingRequest['BookingRequestID'])); ?>" method="post" name="WADAUpdateForm" id="WADAUpdateForm">
change that so the action posts to itself
<form action="BookingRequestDM_Update.php?BookingRequestID=<?php echo(rawurlencode($row_WADABookingRequest['BookingRequestID'])); ?>" method="post" name="WADAUpdateForm" id="WADAUpdateForm">