I am new to working with Google API but I have a project that requires me to access their domain to find a user's manager by email. Before I started on the code I wanted to set everything up so I followed the example file for PHP. I was able to get it to work but had some issues with refreshing the token once it expired and research pushed me towards using a Service Account, as this is a server cron script and I don't want to deal with any user interactions.
I created the Service Account, enabled G Suite Domain-wide Delegation, and added access for: https://www.googleapis.com/auth/admin.directory.user.readonly
I get a Google_Service_Exception with my script. 
The response is:
{
 "error": {
  "errors": [
   {
    "domain": "global",
    "reason": "notFound",
    "message": "Domain not found."
   }
  ],
  "code": 404,
  "message": "Domain not found."
 }
}
I am assuming this means it doesn't know the accounts domain but I don't see how I can resolve this. I assume that if this was a permissions issue, Google would tell me. I tried searching online but no luck as the issues I found were using a different method and the fixes weren't something that could be done on the Service Account. I am stuck right now so I hope a push in the right direction will get me on track.
This is the test script I am using:
<?php
require_once( __DIR__. '/vendor/autoload.php' );
define('CREDENTIALS_PATH', '/path/to/service_account.json');
define('SCOPES', implode(' ', array(
        Google_Service_Directory::ADMIN_DIRECTORY_USER_READONLY)
));
date_default_timezone_set('America/New_York');
/**
 * Returns an authorized API client.
 * @return Google_Client the authorized client object
 */
function getClient() {
    $client = new Google_Client();
    $client->setApplicationName('TestingApp');
    $client->setAuthConfig(CREDENTIALS_PATH);
    $client->setScopes(SCOPES);
    return $client;
}   
// Get the API client and construct the service object.
$client = getClient();
$service = new Google_Service_Directory($client);
// Print the first 10 users in the domain.
$optParams = array(
    'customer' => 'my_customer',
    'maxResults' => 10,
    'orderBy' => 'email',
);
$results = $service->users->listUsers($optParams);
if (count($results->getUsers()) == 0) {
    print "No users found.\n";
} else {
    print "Users:\n";
    foreach ($results->getUsers() as $user) {
        printf("%s (%s)\n", $user->getPrimaryEmail(),
            $user->getName()->getFullName());
    }
}
My service_account.json contains (cleaned obviously)
{
    "type": "service_account",
    "project_id": "PROJECT_ID",
    "private_key_id": "PRIVATE_KEY_ID",
    "private_key": "PRIVATE_KEY",
    "client_email": "SERVICE_ACCOUNT_EMAIL.iam.gserviceaccount.com",
    "client_id": "CLIENT_ID",
    "auth_uri": "https://accounts.google.com/o/oauth2/auth",
    "token_uri": "https://accounts.google.com/o/oauth2/token",
    "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
    "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/SERVICE_ACCOUNT_IDENTIFIER.iam.gserviceaccount.com"
}
Thanks for any assistance on this.
 
     
    