Refresh token is not provided.

Refresh token is not provided.

I am using PHP SDK to implement zoho api's in laravel5.8,
I have done as per document, let me know what doing wrong. Access token, refresh token, expiry_time is storing in database but dont know how to send this refresh token to get access token.
Here my code goes,

<?php

namespace App\Http\Controllers;

use Illuminate\Http\Request;
use zcrmsdk\crm\setup\restclient\ZCRMRestClient;
use zcrmsdk\crm\crud\ZCRMModule;
use zcrmsdk\crm\setup\org\ZCRMOrganization;
use zcrmsdk\oauth\ZohoOAuth;
require 'vendor/autoload.php';
use App\Oauthtokens;

class CRMController extends Controller
{
    public function __construct()
    {

        $configuration=array(
            "client_id"=>"1000.XXXXXXXXXXXXXXXXXXXX",
            "client_secret"=>"XXXXXXXXXXXXXXXXXXXXX",
            "redirect_uri"=>"redirect_url",
            "currentUserEmail"=>"my_zoho_mail_id",
            "accounts_url"=>"https://accounts.zoho.in",
            //"token_persistance_path"=>"file_path",
            "sandbox"=>"false",
            "access_type"=>"offline",
            "apiBaseUrl"=>"www.zohoapis.in",
            //"persistence_handler_class"=>"ZohoOAuthPersistenceHandler",
            "applicationLogFilePath"=>"file_path",
            "userIdentifier"=>"my_zoho_mail_id",
        );

        //access token from grant token
        ZCRMRestClient::initialize($configuration);

        $oAuthClient = ZohoOAuth::getClientInstance(); 
        $grantToken = "1000.b69cdd631109696285dab61223af8599.8328954eb74964a7b174e2c4d35af6ad"; 
        $oAuthTokens = $oAuthClient->generateAccessToken($grantToken);

    }
     public function getUser(){

        try{
            $token = Oauthtokens::orderby('id','desc')->first();
            $refreshToken = $token->refreshtoken;

            $zcrmModuleIns = ZCRMModule::getInstance("Customers");
            $bulkAPIResponse=$zcrmModuleIns->getRecords();
            $recordsArray = $bulkAPIResponse->getData(); // $recordsArray - array of ZCRMRecord instances

            return $recordsArray;
        }catch(ZohoOAuthException $e){
            return $e;
        }
     }
}