[google-cloud-sql-discuss] Google_Service_SQLAdmin notauthorized error - howto fix?

Getting a notauthorized error when I try to use the sqlinstances.php example from https://developers.google.com/api-client-library/php/auth/service-accounts#sqlinstancesphp to get a list of my instances.  I added scopes (and authorized using API manager).  What am I doing wrong here please?

php sqlinstances.php

Fatal error: Uncaught exception 'Google_Service_Exception' with message '{
 "error": {
  "errors": [
   {
    "domain": "global",
    "reason": "notAuthorized",
    "message": "The client is not authorized to make this request."
   }
  ],
  "code": 403,
  "message": "The client is not authorized to make this request."
 }
}

and here is the code:

<?php

// https://developers.google.com/api-client-library/php/auth/service-accounts#sqlinstancesphp

// Autoload Composer.
require_once __DIR__ . '/vendor/autoload.php';
putenv('GOOGLE_APPLICATION_CREDENTIALS=/path/to/service-account.json');

$client = new Google_Client();
$client->useApplicationDefaultCredentials();
$client->addScope('https://www.googleapis.com/auth/cloud-platform');
$client->addScope('https://www.googleapis.com/auth/compute');
$client->addScope('https://www.googleapis.com/auth/compute.readonly');
$client->addScope('https://www.googleapis.com/auth/sqlservice.admin');

$sqladmin = new Google_Service_SQLAdmin($client);

// Project ID of the project for which to list Cloud SQL instances.
$project = 'IDofMyProject';  // TODO: Update placeholder value.
$optParams = [];
$response = $sqladmin->instances->listInstances($project, $optParams)->getItems();

echo json_encode($response) . "\n";
?>

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