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The Server-to-Server (S2S) UPI Collection integration eliminates redirection hops by validating the VPA and initiating transactions directly from your backend. Deliver a seamless, secure checkout experience for your customers.

Validate VPA

Ensure the customer’s VPA is valid before proceeding

Initiate Payment

Create a UPI collect transaction via server-to-server API

Check Status

Poll the Verify Payment API for real-time updates

Server Callback

Receive asynchronous status updates via webhook

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Prerequisites

Before you begin, ensure you have:
  • Merchant Key & Salt: Your EximPe merchant key and salt for hash generation.
  • Callback URL: A publicly accessible endpoint configured in your EximPe dashboard for S2S callbacks.
  • HTTP Client: Ability to perform HTTPS GET and POST requests from your server.
  • JSON & Hashing: Familiarity with JSON request bodies and SHA-512 hash computation.

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Integration Steps

The integration consists of four steps:
  1. Validate VPA
  2. Initiate Payment
  3. Check Transaction Status
  4. Server-to-Server Callback
Process Flow image.png

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Step 1: Validate VPA

This web service will let you validate VPA if it is a valid VPA or not. After the customer enters VPA on your website, you need to call this API to check for VPA validation. If VPA is valid, you need to proceed with the next step.

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Sample Request

curl --location 'https://api-pacb.eximpe.com/pg/vpa/validate/' \
--header 'Content-Type: application/json' \
--header 'Accept: application/json' \
--header 'x-client-id: <api-key>' \
--header 'x-client-secret: <api-key>' \
--header 'x-merchant-id: <api-key>' \
--data '{"vpa": "jake@oksbi"}'

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Response

{
    "success": true,
    "message": "VPA validated successfully",
    "data": {
        "vpa": "jake@oksbi",
        "is_valid": true
    }
}
Collect the response in the UPI Collection under API Reference. The response for the S2S payment request is not similar to Merchant Hosted or PayU Hosted Checkout. For description of response parameters, refer to Additional Info for Payment APIs.  

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Step 2: Initiate the payment to EximPe

To start with, the request is raised from the Merchant to PayU with the required transaction mandatory/optional parameters. This needs to be a server-to-server curl call request 
curl -X POST https://api-pacb.eximpe.com/payment/s2s/upi \
  -H "Content-Type: application/json" \
  -H "X-Client-Key: YOUR_CLIENT_KEY" \
  -d '{
    "amount": "1000.00",
    "collection_mode": "s2s",
    "upi_flow_type": "collection",
    "currency": "INR",
    "reference_id": "S2SC_9PU3P4",
    "vpa": "john.doe@payu",
    "upi_app_name": "others",
    "mop_type": "UPI",
    "buyer": {
      "name": "John Doe",
      "email": "[email protected]",
      "phone": "+919876543210",
      "address": {
        "line_1": "123 Main Street",
        "line_2": "Apt 4B",
        "city": "City",
        "state": "State",
        "postal_code": "123456"
      },
      "ip_address": "192.168.1.100",
      "user_agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.124 Safari/537.36"
    },
    "product": {
      "name": "Sample Product",
      "description": "This is a sample product description",
      "hs_code": "98051000",
      "hs_code_description": "Portable automatic data processing machines",
      "type_of_goods": "goods"
    },
    "invoice": {
      "number": "INV_1T2N7B",
      "date": "2025-07-08"
    }
  }
For the S2S UPI Collection request, you must include these additional parameters beyond the standard checkout fields:
  • collection_mode: must be set to "s2s"
  • upi_flow_type: must be set to "collection"
  • vpa: the customer’s UPI ID (e.g. "john.doe@payu")
  • upi_app_name: the chosen UPI app identifier (e.g. "others")
  • buyer.ip_address: the customer’s device IP address
  • buyer.user_agent: the customer’s browser or app user-agent string

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Step 3: Check UPI transaction status

Check the UPI transaction status using the Verify Order API API. For more information, refer to Verify Order API

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Step 4: Check the S2S callback response

EximPe can also send a server-to-server callback response whenever the transaction status gets updated. For more information, see the Payment Successful response
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