PHP中的重定向不会加载我的链接？

I have 2 php files.

The first one handles the link and stuff. Here is a preview my code:

<?php
    session_start();

     $link=$_GET['redirect'];
        if ($link == '1'){
            $_SESSION['link'] = 'https://www.google.com/';
            header('Location: selection_handler.php');
            exit;
        }
        if ($link == '2'){
            $_SESSION['link'] = 'https://www.facebook.com/';
            header('Location: selection_handler.php');
            exit;

        }
        if ($link == '3'){
             $_SESSION['link'] = 'https://www.twitter.com/';
            header('Location: selection_handler.php');
            exit;
        }
?>

This is my selection_handler.php

<?php
    session_start();
    $link= $_SESSION['link'];

    if(isset($_SESSION['user_id']))
    {
        header("Location: " .$link);
        exit;
    }
    else
    {
        echo  $_SESSION['link'];
    }
?>

user_id would be handled later so by default, i would get the echo of the link from the session, right? that works properly but when i try to test setting a value for the user_id, i see my browser trying to load the link. It says 'Resolving host... Waiting for [insert link selected]' but doesnt fully continue to the site but instead im shown a blank page?

UPDATE: I tried changing the header to ('Location: https://www.google.com') instead of getting from the variable but im still getting a blank page