Unable to remove label in GMAIL PHP API - php

Question

I am working on a project where I have several labels associated with every email. I want to remove the labels using gmail PHP API. I have followed the documentation and I have done all the steps. But, I do not know why I get Error, when I try to remove the label.
This is the code that is associated with the project. Please help me with any thoughts.
$client_id = 'aoppedisano#tecnavi.com';
$service_account_name = 'anthony#teak-truck- 130612.iam.gserviceaccount.com';
$key_file_location = 'anthony.p12';
$userid_from='aoppedisano#tecnavi.com';
$client = new Google_Client();
var_dump($client);
$client->setScopes(array('https://www.googleapis.com/auth/gmail.modify'));
$client->setApplicationName("Client_Library_Examples");
if (isset($_SESSION['service_token'])) {
$client->setAccessToken($_SESSION['service_token']);
}
$key = file_get_contents($key_file_location);
$cred = new Google_Auth_AssertionCredentials(
$service_account_name,
array(
/*
'https://www.googleapis.com/auth/gmail.send',
'https://www.googleapis.com/auth/gmail.compose',
'https://www.googleapis.com/auth/gmail.modify',
*/
'https://www.googleapis.com/auth/gmail.readonly'
),
$key
);
//var_dump($cred);
$cred->sub=$userid_from; //<-- Important!
$client->setAssertionCredentials($cred);
if ($client->getAuth()->isAccessTokenExpired()) {
$client->getAuth()->refreshTokenWithAssertion($cred);
}
$service = new Google_Service_Gmail($client);
$messageId=$_REQUEST["id"];
$userId = 'me';
$optParamsGet = [];
$optParamsGet['format'] = 'full';
$message = $service->users_messages->get('me',$messageId,$optParamsGet);
$labelsToRemove=$_REQUEST['label'];
$labelsToAdd=[];
$message=modifyMessage($service,$userId, $messageId, $labelsToAdd, $labelsToRemove);
function modifyMessage($service, $userId, $messageId, $labelsToAdd, $labelsToRemove) {
$mods = new Google_Service_Gmail_ModifyMessageRequest();
$mods->setAddLabelIds($labelsToAdd);
$mods->setRemoveLabelIds($labelsToRemove);
try {
$message = $service->users_messages->modify($userId, $messageId, $mods);
print 'Message with ID: ' . $messageId . ' successfully modified.';
return $message;
} catch (Exception $e) {
print 'An error occurred: ' . $e->getMessage();
}
}

Answer 1

As given in Standard Error Responses for Google APIs, 403: insufficientPermissions error code means that the authenticated user does not have sufficient permissions to execute this request.
To delete labels, you should have this scope code in your permissions:
https://www.googleapis.com/auth/gmail.labels
For more details about scopes, please go through Choose Auth Scopes.