Uncaught Error: Class not found

I am using this package in Raw PHP.

https://github.com/osiset/Basic-Shopify-API#installation

After installing I get the vendor folder and that is installed perfectly. Please check this image below: https://ibb.co/M7NNJ7k

In the same directory of vector, I have a file for searching. Trying to access that Package Class. But it giving me erorr:

require './vendor/autoload.php'; 

use Osiset\BasicShopifyAPI\BasicShopifyAPI;
use Osiset\BasicShopifyAPI\Options;
use Osiset\BasicShopifyAPI\Session;

Error:

Fatal error: Uncaught Error: Class "Osiset\BasicShopifyAPI\Options" not found in search_graphql.php:213

Can't find any reason. Anyone can help me?