---
page_source: https://juspay.io/in/docs/upi-merchant-stack/docs/overview/introduction
page_title: Introduction
---


# Introduction



[Video](https://dth95m2xtyv8v.cloudfront.net/tesseract/assets/upi-merchant-stack/Walkthrough%20of%20different%20sections%20in%20documentation.mov)



Welcome to the UPI PSP Backend API Reference Document. This doc consists of the comprehensive information about our Server-to-Server APIs. We use **application/json**  content type for our request and response.

This documentation is designed to guide you through each API in detail. From API descriptions to the step-by-step flow, everything you need is outlined in the sections below. Each section includes crucial information about the API's structure, including the Request and Response body specifications.

Before you dive into the APIs, we recommend familiarizing yourself with the [Request](https://docs.juspay.in/upi-merchant-stack/docs/overview/api-guide#Request-Structure) and [Response](https://docs.juspay.in/upi-merchant-stack/docs/overview/api-guide#Response-Structure) structure. This will provide you with essential insights into prerequisites and overall formatting, ensuring a smooth integration process.

**The docs covers different use cases of a merchant for payments processing** **:** 

* 1st **[Transactions](https://docs.juspay.in/upi-merchant-stack/docs/transactions)** **(Payins & Refunds)**  where merchants want to acquire/collect money from user on **demand basis** for one-time payments & refund against original transaction.
* 2nd **[Mandates](https://docs.juspay.in/upi-merchant-stack/docs/mandates)** **(UPI AUTOPAY)**  where merchants want to acquire/collect money from user on **regular basis**  for recurring payments by one-time mandate creation(registration). This would mostly be used for Subscriptions, Bill Payments, Investments, Insurance Payments, Donations, Wallet Top-ups etc.
* 3rd **[Payouts](https://docs.juspay.in/upi-merchant-stack/docs/payouts)**  where merchants want to disburse money from Merchant Accounts to Customer Accounts instantly. It can be also used for Customer Account Verification via Penny Drop. This would mostly be used for Rewards, Cashbacks, Incentives etc.
* 4th **[Sub-Merchants](https://docs.juspay.in/upi-merchant-stack/docs/submerchants)**  where parent merchant want to enable its different LOBs(Line of Business) or franchise/branches to acquire/collect money via Intent/Collect or unique QR codes via any UPI app. Sub-merchant payments can be one-time or recurring depending upon use case & integration.