getting error undefine index in uploading score

It looks like the error is that you are never defining the variable $hash, and that the indexes for name and score are never set.

Looking at the tutorial, I noticed a line that says, "Please! This code need to be tested. Tested, confirmed not working. Use snippet above. " I would probably recommend trying the first code snippet example, instead of the second one, and seeing where that takes you.

Although this response is quite late, this is for those of you who come to this particular question also looking for an answer.

As Jawchewa mentioned, $hash was never defined as well as the indexes when executing the command. Here is an updated version that I have modified and tested.

 <?php
         // Configuration
         $hostname = 'INSERT_HOSTNAME_HERE';
         $username = 'INSERT_USERNAME_HERE';
         $password = 'INSERT_PASSWORD_HERE';
         $database = 'INSERT_DATABASE_HERE';
  
         $secretKey = "INSERT_SECRET_KEY_HERE"; // Change this value to match the value stored in the client javascript below 
  
         try {
             $dbh = new PDO('mysql:host='. $hostname .';dbname='. $database, $username, $password);
         } catch(PDOException $e) {
             echo '<h1>An error has ocurred.</h1><pre>', $e->getMessage() ,'</pre>';
         }
 
         $username = $_GET['name'];
         $userscore = $_GET['score'];
 
         $realHash = md5($_GET['name'] . $_GET['score'] . $secretKey);
         $hash = $_GET['hash'];
  
         if($realHash == $hash) { 
             $sth = $dbh->prepare('INSERT INTO scores VALUES (null, :username, :userscore)');
             try {
                 $sth->execute(['username' => $username, 'userscore' => $userscore]);
             } catch(Exception $e) {
                 echo '<h1>An error has ocurred.</h1><pre>', $e->getMessage() ,'</pre>';
             }
         } 
 ?>

Hopefully someone finds this useful :)