Invalid_client when using zohobooks API

Invalid_client when using zohobooks API

API reference: OAuth | Zoho Books | API Documentation
I want to do invoice automation using Zoho APIs and for that, I needed an authentication token. 
I followed the steps mentioned in the above documentation.

1) Create a client to get the client id and client secret.
2) Make a GET request to obtain code. I was successfully able to redirect to the URL and the code was available there.
3) This is the step I am facing a problem in. To get the token we have to make a POST request with the client ID, secret, and code obtained from the previous step. When I make the POST request it sends an error saying client_invalid. Is there something I am doing wrong?

Best Regards,
Ishant