how can we integration paytm pg on codeigniter 3 as our need

[jaipalsin]

I want to integrate Paytm into the MVC (Codeigniter 3 Framework) pattern
Paytm Payment Gateway supports checksum generation and verification utility Which I want to use as per my requirement.
I have also completed the checksum validation utility and have set up the environment by creating a Paytm library on MVC pattern but I do not understand how to create the form as I want. how to implement on Paytm PG kit code as my requirement

My form requirement is as follows:
I want to use the PG Kit code received from Paytm in my project as per my requirements. I want when the user adds an item to the cart and goes to the checkout button, the user is redirected to the shipping data(mobile, name, address, pin code, street, etc ) submission page. Where after completing of submitting the shipping data, as per Paytm credentials, the user will be redirected to the callback page where he will make the payment with the total amount. Once payment is completed, the user should be shown complete order details including shipping data and information obtained from the API response. How can this be done using 'session/rest'? Please provide me the code or logic for this so that I can understand it in depth in a better way

Paytm integration source code: https://github.com/paytm/Paytm_PHP_Sample
checksum implementation source code https://business.paytm.com/docs/checksum-implementation?ref=checksumdocument