Uncaught zcrmsdk\crm\exception\ZCRMException Caused by:'invalid oauth token'

Hello Zoho Team,

I am facing this issue again and again when I try to access the Leads module.

I generated the grant token with this scope "ZohoCRM.modules.ALL".

This is my configuration

$configuration=array(

"client_id"=>$client_id,

"client_secret"=>$client_secret,

"redirect_uri"=>$redirect_url,

"currentUserEmail"=>$user_email_id,

"access_type"=>$access_type,

"api_domain"=>"https://www.zohoapis.com",

"accounts_url"=>"https://accounts.zoho.in"

);

$rest=ZCRMRestClient::getInstance();

$rest->initialize($configuration);

$oAuthClient = ZohoOAuth::getClientInstance();

$grantToken = '1000.30989f8fe48c884a6f046c6aa04fcbc5.a4f63a6d8df5228fd8330dd96ab647f1'; //hard coded

$oAuthTokens = $oAuthClient->generateAccessToken($grantToken);

everything goes well till here

$module=$rest->getModule("Leads")->getData(); // this line give me the error;

I am new to zoho and really need your help. Please reply asap.