$("#OK").click(function()
    {
        unsubscribeMember();
         window.location.href="signup-for-event.php?memId=" + <?php echo $_SESSION['memberId'] ?>;
    });

function unsubscribeMember()
{
    var data = "memId=" + <?php echo $_SESSION['memberId'];?> + "&actID=" + <?php echo $_GET['actID']; ?> ;
    alert(data);

    $.ajax({
        dataType: 'json',
        url: 'json-responses.php?fct=deleteMemberFromActivity',
        data: data,
        cache: false
    });
}

if ($_GET['fct'] == 'deleteMemberFromActivity')
{
    $result = deleteMemberFromActivity($connectionObject, $_GET['actID'], $_GET['memId']);
    echo $result;
}

function deleteMemberFromActivity($PDOdbObject, $actId, $memberId)
{
    $deleteSignUpsSQL = "DELETE FROM 'member_activity' WHERE 'activity_id' = ? AND 'member_id' = ?";
    $stmt = $PDOdbObject->prepare($deleteSignUpsSQL);
    $stmt -> execute([$actId, $memberId]);
    $affected_rows = $stmt->rowCount();
    return $affected_rows;
}