Catalog REST API extension - Getting 'You do not have permission to access the API!'

Hello,
I have installed the catalog rest api extension https://www.opencart.com/index.php?rout ... r_rating=1 in OpencCart(2.3.0.2). My requirement is
1. Login to the store using REST API (http://127.0.0.1?route=api/login)
2. Fetch the products and categories using that token which will get in the response.

I can able to access all 3 APIs in the POSTMAN. But when I trying to fetch it from my Ruby On Rails application using RESTCLIENT, I am getting this error
{"error"=>{"warning"=>"Warning: You do not have permission to access the API!"}} . I have given full permissions to all users and also selected API users on the Home > Stores > Settings > API User section.

I am suck here because I have new to PHP and OpenCart. Please help me to fix this issue ASAP?
Thanks

But when I trying to fetch it from my Ruby On Rails application using RESTCLIENT, I am getting this error
{"error"=>{"warning"=>"Warning: You do not have permission to access the API!"}}

What does that explain and how relevant is your inquiry involved with Opencart in particular?