Hi, @asmecher,
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
Thank you.