Yes this is possible to integrate Paytm in shopify.
Dashborad->Setting->Payment Providers->Alternative payment method
Select paytm from this method.
I have already integrated paytm on shopify but I want to create custom checkout payment page on store. Is it possible?
You can take this as a reference :- https://developer.paytm.com/docs/v1/custom-checkout
This is what I want.