Send Users to a Mailchimp List w/ Custom Fields in Pure PHP

mailchimp_user_automation.php

<?php

$API_KEY = '[Mailchimp API Key Goes Here]';
$LIST_ID = "[Mailchimp List ID Here]";
$AUTH_HEADER = "Authorization: Basic ".base64_encode("anystring:".$API_KEY)."\r\nContent-type: application/x-www-form-urlencoded\r\n";

// Prob. fetched from db..
$list_of_users = [
  (object)["first" => "John", "last" => "Smith", "email" => "john@example.com", "color" => "red"],
  (object)["first" => "Jane", "last" => "Doe", "email" => "jane@example.com", "color" => "blue"]
];

foreach($list_of_users as $user){
  $email = $user->email;
  $email_hash = md5($email);

  $merge_fields = [
    'FNAME' => $user->first,
    'LNAME' => $user->last,
    'COLOR' => $user->color // Custom fields have to be added in list settings first
  ];

  try {
    // If the $url exists then we'll send a PATCH request to update 
    $url = "https://us2.api.mailchimp.com/3.0/lists/{$LIST_ID}/members/{$email_hash}";
    $context = stream_context_create([ 'http' => [
        'header'  => $AUTH_HEADER,
        'method'  => "GET"
      ]
    ]);

    if(@file_get_contents($url, true, $context)) {
      $subscriber_info = json_encode([
        'email_address' => $email,
        'status' => "subscribed",
        'merge_fields' => $merge_fields
      ]);

      $context = stream_context_create([ 'http' => [
          'header'  => $AUTH_HEADER,
          'method'  => "PATCH",
          'content' => $subscriber_info
        ]
      ]);

      $resp = @file_get_contents($url, true, $context);
    } else {
      throw new Exception;
    }

  } catch (Exception $error){
    // They didn't exist so we can create a new subscriber member

    $url = "https://us2.api.mailchimp.com/3.0/lists/{$LIST_ID}/members/";
    
    $subscriber_info = json_encode([
      'email_address' => $email,
      'status' => "subscribed",
      'merge_fields' => $merge_fields
    ]);

    $context = stream_context_create([ 'http' => [
        'header'  => $AUTH_HEADER,
        'method'  => "POST",
        'content' => $subscriber_info
      ]
    ]);

    $resp = @file_get_contents($url, true, $context);
  }
}