Undefined type 'Google_Service_Oauth2' intelephense(1009) PHP

one text

I currently modify my php script using namespace. I've done with the scripts but there are problem with Google API package

// create Client Request to access Google API
        $client = new \Google_Client(); => THIS ONE WORKS
        $client->setClientId($clientID);
        $client->setClientSecret($clientSecret);
        $client->setRedirectUri($redirectUri);
        $client->addScope("email");
        $client->addScope("profile");

        $accessToken = $key;

        // Get $id_token via HTTPS POST.
        try{
            $arrToken = $client->setAccessToken($accessToken);
            // get profile info
            $google_oauth = new \Google_Service_Oauth2($client); => IT DOESNT
            $google_account_info = $google_oauth->userinfo->get();
            $checkEmail =  $google_account_info->email;
            $name =  $google_account_info->name;
            $googleId = $google_account_info->id;           
        }

Here is the error

Undefined type 'Google_Service_Oauth2' intelephense(1009)

If I do not use namespace, it has no problem. This one really weird.