Creating SDK for Android Payment Script

I have a payment gateway script to be working on android app. I want to make it easy for others to integrate it in their own app via SDK or API. like Razorpay, Paypal or any other payment gateways have. All the details passing through the implented SDK remotely anywhere should be accessible on the website dashboard.
The SDK implemented in the remote client App should be able to turn off in case I dont want to serve the client anymore.