I have the same query and my PKP OJS version is [ojs-3.2.1-3].
I would like to integrate our local UPI payment gateway into the website in replacement to PayPal.
Some of the payment gateway that helps us get UPI transactions are:
RazorPay- Install Razorpay PHP SDK
PayU- PayUmoney PHP integration guide - PayU Developer Guide | Payment Gateway Integration
In order to do this, there would likely have to be a plugin created. To get a sense of what is involved in this, you can check out our plugin guide: Plugin Guide - Language Selection