the authentiocate user behaivor is set to store the member ID as a session variable:
"sessionColumns" => explode($WA_Auth_Separator,"MemberContactID".$WA_Auth_Separator."MemberID"),
"sessionNames" => explode($WA_Auth_Separator,"MemberContactID".$WA_Auth_Separator."MemberID"),
but think about order of operations. this code block is setting a list of perameters that are going to be sent into the WA_AuthenticateUser function
you cant at the same time tell the function to lookup the session variable, and tell it to use the session in the success redirect:
"successRedirect" => "../events/booktickets.php?EventID=".$_GET['EventID']."&MemberID=".$_SESSION['MemberID'],
the session hasn't been looked up yet.
leave the success redirect blank, and add header function after the WA_AuthenticateUser function
<?php header("Location: ../events/booktickets.php?EventID=".$_GET['EventID']."&MemberID=".$_SESSION['MemberID']); ?>