Payin P2C Seamless Wallet Integration

UPI is a set of APIs developed by NPCI to enable instant online payments. It simplifies immediate payments via mobile devices. Payments can be initiated by both the sender (payer) and the receiver (payee) and can be completed using virtual payment addresses, Aadhaar integration, mobile numbers, and more. The payer’s smartphone can securely capture credentials for these transactions.

Merchant Onboarding: The merchant must provide the following information for onboarding in both the UAT and production environments:

IP Address (For dynamic IPs, please provide the range of IP addresses).
Merchant Callback URL to post the final transaction status from our system.

Once the merchant provides the required technical details, we will complete the necessary back-office configurations and provide a Merchant ID (MID/PID).

Let's see how it works:

Merchant sends a payment collection request through our API, they need to provide the customer's wallet_type, order_id, pid, amount, name, email, and phone details.
PAYMENT REQUEST : Upon receiving the request in the correct format, we will share a payment redirect_url that redirects the customer to the selected wallet's payment screen.
CALLBACK : After the payment is verified, you will receive callback data at the provided callback URL.
STATUS POLLING : You can confirm or check the payment status by calling the polling_api at any time and update your system accordingly.

PAYMENT REQUEST :

Before proceeding with this section, please ensure you have reviewed the Basic Workflow of the system. This page outlines how to send a payment request effectively.

Important Note: All requests must originate from whitelisted IP addresses. Please verify that your IP is properly whitelisted before initiating any requests.

Payment Request

POST https://<domain>/api/request.php

Merchant makes a payment request.

Headers

Name

Value

Content-Type

application/json

Body

Name

Type

Description

pid

string

provided MID/PID

order_id

string

unique order id

amount

integer

amount

wallet_type

string

Wallet type, allowed values are {'Nagad','Rocket','bKash','Upay'}

phone

string

Customer phone number

email

string

Customer email address

name

string

Customer contact name

{
    "pid": "0951272386617",
    "order_id": "MXmzie9932idwq3",
    "amount": "43",
    "upi_id": "testpaybank123@upi",
    "wallet_type": "bKash"
    "phone":"9895000000",
    "name":"exampleName",
    "email":"[email protected]"
}

Note: wallet_type is mandatory and important for Bangladesh to work properly.

Sample Response Body

{
    "ref_code": "491836c1346f84516af3179e6b14e54f6914ab3e4eb59a62b6d2913781152c6d",
    "wallet_id": "",
    "wallet_type": "bKash",
    "amount": 43,
    "status": "success",
    "wallet_url": "https://payment.bkash.com/?paymentId=TR00115SWdn0W1727439860411&hash=2vsy-Gcek8U0OZ-j!DqF2VJs6Oux4tJyNrbM).o!5DTL0iZZs*fgAz4OrJGAjymdY0z7t7SKte1App*J4r*YpgSeaWoI6szVTpLK1727439860411&mode=0011&apiVersion=v1.2.0-beta/"
}

CALLBACK

We invoke your callback URL with callback data whenever there is a status change against the transaction.

Valid Transaction status are:

Approved
Declined
Late Approved
Pending
User Timed Out
Cancelled
Failed
Amount Mismatch

The most famous transaction changes are (but not limited):

Pending=>Approved
Pending=>Declined
Pending=>User Timed Out
User Timed Out=>Late Approved

The callback landing page must be set up on your server at a secret path, but it should be publicly accessible from our whitelisted IP. (Ensure that it is only accessible from our server IP.)

In the POST body, the following properties will be provided in JSON format:

Name

Type

Description

order_id

string

Your order id shared

requested_amount

string

requested amount

received_amount

string

received amount

bank_ref

string

transaction reference/bank reference/UTR if available

ref_code

string

unique code for the transaction

status

string

status of payment at this time

post_hash

string

signature post hash for security verification

Note:

please consider received_amount for final transaction processing

Follow the steps to verify the integrity of received data:

Capture and Decode the Payload

Capture the raw JSON data from the POST body and decode it.

$data = file_get_contents("php://input");
$array = json_decode($data,  true);

Extract and Decode the post_hash

The post_hash field in the JSON payload is a Base64-encoded string. You must Base64-decode it to get the raw binary data needed for decryption.

// Get the Base64 string from the array
$post_hash_base64 = $array['post_hash'];
 
// Decode it to get the raw binary ciphertext
$ivHashCiphertext = base64_decode($post_hash_base64);

Decrypt the Binary Data to get the Remote Hash

Pass the raw binary data (not the Base64 string) to the decrypt function along with your secret key.

//$secret_key is your provided SECRET KEY
$remote_hash = decrypt($ivHashCiphertext, $secret_key);

The decrypt function for your language is provided in the reference section below.

function decrypt($ivHashCiphertext, $password) 
{    
    $method = "AES-256-CBC";    
    $iv = substr($ivHashCiphertext, 0, 16);    
    $hash = substr($ivHashCiphertext, 16, 32);    
    $ciphertext = substr($ivHashCiphertext, 48);    
    $key = hash('sha256', $password, true);    
    if (!hash_equals(hash_hmac('sha256', $ciphertext . $iv, $key, true),$hash)) 
    return null;    
    return openssl_decrypt($ciphertext, $method, $key,    		    
    OPENSSL_RAW_DATA, $iv);                               
}

const crypto = require('crypto');

/**
 * @param {Buffer} ivHashCiphertext - The raw binary data (Buffer) after Base64-decoding.
 * @param {string} password - Your secret key.
 * @returns {string|null} The decrypted plaintext or null on failure.
 */
function decrypt(ivHashCiphertext, password) {
    const method = 'aes-256-cbc';

    // Extract the initialization vector (first 16 bytes)
    const iv = ivHashCiphertext.slice(0, 16);

    // Extract the hash (next 32 bytes)
    const hash = ivHashCiphertext.slice(16, 48);

    // Extract the ciphertext (remaining bytes)
    const ciphertext = ivHashCiphertext.slice(48);

    // Generate the key using SHA-256 hash of the password
    const key = crypto.createHash('sha256').update(password, 'utf8').digest();

    // Compute HMAC-SHA256 of (ciphertext || iv) using the key
    const hmac = crypto.createHmac('sha256', key)
        .update(Buffer.concat([ciphertext, iv]))
        .digest();

    // Compare the computed HMAC with the extracted hash
    if (!crypto.timingSafeEqual(hmac, hash)) {
        return null; // Hashes do not match; return null
    }

    try {
        // Decrypt the ciphertext using AES-256-CBC
        const decipher = crypto.createDecipheriv(method, key, iv);
        const plaintext = Buffer.concat([
            decipher.update(ciphertext),
            decipher.final()
        ]);
        return plaintext.toString('utf8'); // Return the decrypted text as a UTF-8 string
    } catch (err) {
        // Decryption failed; return null
        return null;
    }
}

import hashlib
import hmac
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
from cryptography.hazmat.primitives import padding

def decrypt(ivHashCiphertext, password):
    """
    Decrypts the iv/hash/ciphertext blob.
    
    :param ivHashCiphertext: The raw binary data (after base64-decoding).
    :param password: Your secret key string.
    :return: The decrypted plaintext string, or None on failure.
    """
    try:
        # 1. Extract the components
        iv = ivHashCiphertext[:16]
        hash_val = ivHashCiphertext[16:48]
        ciphertext = ivHashCiphertext[48:]

        # 2. Generate the key
        key = hashlib.sha256(password.encode('utf-8')).digest()

        # 3. Verify the HMAC
        computed_hash = hmac.new(key, ciphertext + iv, hashlib.sha256).digest()

        if not hmac.compare_digest(computed_hash, hash_val):
            return None

        # 4. Decrypt the ciphertext
        backend = default_backend()
        cipher = Cipher(algorithms.AES(key), modes.CBC(iv), backend=backend)
        decryptor = cipher.decryptor()
        
        # Decrypt and unpad
        # Using PKCS7 unpadder explicitly is more robust
        decrypted_padded_text = decryptor.update(ciphertext) + decryptor.finalize()
        unpadder = padding.PKCS7(algorithms.AES.block_size).unpadder()
        decrypted_text = unpadder.update(decrypted_padded_text) + unpadder.finalize()

        return decrypted_text.decode('utf-8')

    except Exception as e:
        # Catch any error (e.g., bad padding, bad key) and return None
        # print(f"Decryption failed: {e}") # Optional: for debugging
        return None

Compute the Local Hash

Compute the local hash using the MD5 128-bit hashing algorithm. Use the order_id, received_amount, and status received in the callback array for computing the local hash.

// Get the values from the same callback $array
$order_id = $array['order_id'];
$received_amount = $array['received_amount'];
$status = $array['status'];
 
$local_hash = md5($order_id . $received_amount . $status . $secret_key);

Verify Hash

Compare the decrypted $remote_hash from the request and the computed $local_hash.

if ($remote_hash === $local_hash)
{  
    // consider received amount to update  
    // Mark the transaction as success & process the order  
    // You can write code process the order here  
    // Update your db with payment success  
    $hash_status = "Hash Matched";    
}  
else  
{  
    // Verification failed       
    $hash_status = "Hash Mismatch";  
}

Acknowledge the Payment Gateway

To confirm you have received the callback and to prevent our gateway from sending retries, you must do two things:

Respond with an HTTP 200 OK status code.
Respond with a JSON body containing the key "acknowledge" set to the string "yes".

Our system will check for both the 200 status and the {"acknowledge": "yes"} in the response body. If either is missing, we will assume the callback failed and will attempt to send it again.

// --- This is the required acknowledgment ---

// 1. Set the HTTP 200 OK status code
http_response_code(200);

// 2. Prepare the required JSON response body
$response_data = [
    'acknowledge' => 'yes',
    'hash_status' => $hash_status // You can include this for your own logs
];

// 3. Send the response
header('Content-Type: application/json; charset=utf-8');
echo json_encode($response_data);
exit;

STATUS POLLING :

POST https://<domain>/api/status_polling.php

This API is used to poll the status of a particular transaction.

Headers

Name

Value

Content-Type

application/json

Body

Name

Type

Description

Mandatory

pid

string

Provided Merchant ID/PID

Yes

ref_code

string

unique ref_code which is generated in payment request

Yes

post_hash

string

The Base64-encoded encrypted hash. (See steps below).

Yes

Steps to generate post_hash :

Generate the Request post_hash

1.1 Create Plaintext Hash: Concatenate the ref_code, pid, and your secret_key, then create an MD5 hash.

$ref_code = "YOUR_REF_CODE";
$pid = "YOUR_PID";
$secret_key = "YOUR_SECRET_KEY";

$local_hash = md5($ref_code . $pid . $secret_key);

const crypto = require('crypto');

const ref_code = "YOUR_REF_CODE";
const pid = "YOUR_PID";
const secret_key = "YOUR_SECRET_KEY";

const local_hash = crypto
  .createHash('md5')
  .update(ref_code + pid + secret_key)
  .digest('hex');

1.2 Encrypt the Hash: Encrypt the $local_hash using the encrypt function shown below.

$encrypted_hash = encrypt($local_hash, $secret_key);

function encrypt($plaintext, $password) 
{    
    $method = "AES-256-CBC";    
    $key = hash('sha256', $password, true);    
    $iv = openssl_random_pseudo_bytes(16);    
    $ciphertext = openssl_encrypt($plaintext, $method, $key,       
        OPENSSL_RAW_DATA, $iv);    
    $hash = hash_hmac('sha256', $ciphertext . $iv, $key, true);    
    return $iv . $hash . $ciphertext;
}

import hashlib
import hmac
import os
from Crypto.Cipher import AES
from Crypto.Util.Padding import pad, unpad
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
from cryptography.hazmat.primitives import padding as crypto_padding

def encrypt(plaintext, password):
    key = hashlib.sha256(password.encode('utf-8')).digest()
    iv = os.urandom(16)
    
    cipher = AES.new(key, AES.MODE_CBC, iv)
    plaintext_bytes = plaintext.encode('utf-8')
    padded_plaintext = pad(plaintext_bytes, AES.block_size)
    ciphertext = cipher.encrypt(padded_plaintext)
    
    hash_value = hmac.new(key, ciphertext + iv, hashlib.sha256).digest()
    
    return iv + hash_value + ciphertext

const crypto = require('crypto');

function encrypt(plaintext, password) {
    const method = 'aes-256-cbc';
    const key = crypto.createHash('sha256').update(password, 'utf8').digest();
    const iv = crypto.randomBytes(16);

    const cipher = crypto.createCipheriv(method, key, iv);
    let ciphertext = cipher.update(plaintext, 'utf8');
    ciphertext = Buffer.concat([ciphertext, cipher.final()]);

    const hmac = crypto.createHmac('sha256', key);
    hmac.update(Buffer.concat([ciphertext, iv]));
    const hash = hmac.digest();

    // Return the raw binary Buffer
    return Buffer.concat([iv, hash, ciphertext]);
}

1.3 Base64 Encode: Base64-encode the raw binary output from the encrypt function. This final string is your post_hash.

$post_hash = base64_encode($encrypted_hash);

Send the POST Request

Send a POST request containing pid, ref_code, and post_hash as a JSON body , and you will receive a response after validating the data.

PHP (cURL) Example:

<?php
// Your transaction data
$pid = "YOUR_PID";
$ref_code = "YOUR_REF_CODE";
$secret_key = "YOUR_SECRET_KEY";

// --- Step 1: Generate Hash ---
$local_hash = md5($ref_code . $pid . $secret_key);
$encrypted_hash = encrypt($local_hash, $secret_key);
$post_hash = base64_encode($encrypted_hash);

// --- Step 2: Send Request ---
$api_url = "https://<domain>/api/status_polling.php";

$data = [
    'pid' => $pid,
    'ref_code' => $ref_code,
    'post_hash' => $post_hash
];

$ch = curl_init();

curl_setopt($ch, CURLOPT_URL, $api_url);
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($data));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, ['Content-Type: application/json']);

$server_output = curl_exec($ch);
curl_close($ch);

?>

Processing the API Response

The API will respond with a JSON object. If the request is successful and the ref_code is found, it will return the transaction details. If it fails (e.g., bad hash, ref_code not found), it will return an error message.

_{Success Response Parameters}

A successful response will contain the following parameters as JSON body:

order_id

String

Your order ID.

ref_code

String

The unique ref_code for this transaction.

upi_id

String

The UPI ID the payment was made to.

requested_amount

Number

The amount originally requested for the transaction.

received_amount

Number

The final amount confirmed as received.

bank_ref

String

The bank's UTR / reference number, if available.

sender_upi

String

The customer's UPI ID from which the payment was received.

webhook_acknowledged

String

"1" if our server has sent the callback, "0" otherwise.

status

String

The current status of the transaction (e.g., Approved, Pending, Declined, etc).

post_hash

String

A Base64-encoded encrypted hash to verify the integrity of this response.

_{Error Response}

An error response will contain an error key.

{
    "error": "error message"
}

Verify the Response post_hash

Before trusting any data from the response, you must verify its post_hash to ensure the data is from us and has not been tampered with. This verification logic is identical to the logic used for verifying a callback.

You do not need to send an "Acknowledge" response for a status poll.

4.1 Compute the Local Hash

From the JSON response, get the order_id, received_amount, and status. Concatenate them with your secret_key and create an MD5 hash.

// $response_data is the decoded JSON response from /api/status_polling.php
$order_id = $response_data['order_id'];
$received_amount = $response_data['received_amount'];
$status = $response_data['status'];
 
$local_hash = md5($order_id . $received_amount . $status . $secret_key);

// responseData is the parsed JSON response
const order_id = responseData.order_id;
const received_amount = responseData.received_amount;
const status = responseData.status;
 
const local_hash = crypto
  .createHash('md5')
  .update(order_id.toString() + received_amount.toString() + status.toString() + secret_key)
  .digest('hex');

# response_data is the parsed JSON response (a dict)
order_id = response_data['order_id']
# Ensure values are strings for concatenation
received_amount = str(response_data['received_amount']) 
status = response_data['status']
 
local_hash = hashlib.md5((order_id + received_amount + status + secret_key).encode('utf-8')).hexdigest()

4.2 Decrypt the Remote Hash

Get the post_hash string from the JSON response. Base64-decode it, then pass the raw binary data to the decrypt function.

// Get the Base64 string from the response
$post_hash_base64 = $response_data['post_hash'];
 
// Decode it to get the raw binary ciphertext
$ivHashCiphertext = base64_decode($post_hash_base64);
 
// Decrypt using the function from the reference section below
$remote_hash = decrypt($ivHashCiphertext, $secret_key);

const postHashBase64 = responseData.post_hash;
 
// Decode it to get the raw binary buffer
const ivHashCiphertext = Buffer.from(postHashBase64, 'base64');
 
// Decrypt using the function from the reference section below
const remote_hash = decrypt(ivHashCiphertext, secret_key);

import base64

post_hash_base64 = response_data['post_hash']
 
# Decode it to get the raw binary data
ivHashCiphertext = base64.b64decode(post_hash_base64)
 
# Decrypt using the function from the reference section below
remote_hash = decrypt(ivHashCiphertext, secret_key)

The decrypt function for your language is provided in the reference section below.

function decrypt($ivHashCiphertext, $password) 
{    
    $method = "AES-256-CBC";    
    $iv = substr($ivHashCiphertext, 0, 16);    
    $hash = substr($ivHashCiphertext, 16, 32);    
    $ciphertext = substr($ivHashCiphertext, 48);    
    $key = hash('sha256', $password, true);    
    if (!hash_equals(hash_hmac('sha256', $ciphertext . $iv, $key, true),$hash)) 
    return null;    
    return openssl_decrypt($ciphertext, $method, $key,    		    
    OPENSSL_RAW_DATA, $iv);                               
}

const crypto = require('crypto');

/**
 * @param {Buffer} ivHashCiphertext - The raw binary data (Buffer) after Base64-decoding.
 * @param {string} password - Your secret key.
 * @returns {string|null} The decrypted plaintext or null on failure.
 */
function decrypt(ivHashCiphertext, password) {
    const method = 'aes-256-cbc';

    // Extract the initialization vector (first 16 bytes)
    const iv = ivHashCiphertext.slice(0, 16);

    // Extract the hash (next 32 bytes)
    const hash = ivHashCiphertext.slice(16, 48);

    // Extract the ciphertext (remaining bytes)
    const ciphertext = ivHashCiphertext.slice(48);

    // Generate the key using SHA-256 hash of the password
    const key = crypto.createHash('sha256').update(password, 'utf8').digest();

    // Compute HMAC-SHA256 of (ciphertext || iv) using the key
    const hmac = crypto.createHmac('sha256', key)
        .update(Buffer.concat([ciphertext, iv]))
        .digest();

    // Compare the computed HMAC with the extracted hash
    if (!crypto.timingSafeEqual(hmac, hash)) {
        return null; // Hashes do not match; return null
    }

    try {
        // Decrypt the ciphertext using AES-256-CBC
        const decipher = crypto.createDecipheriv(method, key, iv);
        const plaintext = Buffer.concat([
            decipher.update(ciphertext),
            decipher.final()
        ]);
        return plaintext.toString('utf8'); // Return the decrypted text as a UTF-8 string
    } catch (err) {
        // Decryption failed; return null
        return null;
    }
}

import hashlib
import hmac
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
from cryptography.hazmat.primitives import padding

def decrypt(ivHashCiphertext, password):
    """
    Decrypts the iv/hash/ciphertext blob.
    
    :param ivHashCiphertext: The raw binary data (after base64-decoding).
    :param password: Your secret key string.
    :return: The decrypted plaintext string, or None on failure.
    """
    try:
        # 1. Extract the components
        iv = ivHashCiphertext[:16]
        hash_val = ivHashCiphertext[16:48]
        ciphertext = ivHashCiphertext[48:]

        # 2. Generate the key
        key = hashlib.sha256(password.encode('utf-8')).digest()

        # 3. Verify the HMAC
        computed_hash = hmac.new(key, ciphertext + iv, hashlib.sha256).digest()

        if not hmac.compare_digest(computed_hash, hash_val):
            return None

        # 4. Decrypt the ciphertext
        backend = default_backend()
        cipher = Cipher(algorithms.AES(key), modes.CBC(iv), backend=backend)
        decryptor = cipher.decryptor()
        
        # Decrypt and unpad
        # Using PKCS7 unpadder explicitly is more robust
        decrypted_padded_text = decryptor.update(ciphertext) + decryptor.finalize()
        unpadder = padding.PKCS7(algorithms.AES.block_size).unpadder()
        decrypted_text = unpadder.update(decrypted_padded_text) + unpadder.finalize()

        return decrypted_text.decode('utf-8')

    except Exception as e:
        # Catch any error (e.g., bad padding, bad key) and return None
        # print(f"Decryption failed: {e}") # Optional: for debugging
        return None

4.3 Compare the Hashes

Securely compare the local_hash you just computed with the remote_hash you decrypted. If they match, you can trust the data.

if ($remote_hash !== null && hash_equals($local_hash, $remote_hash)) {
    // --- SUCCESS: Data is verified ---
    // You can now trust the data and update your database.
    // echo "Status: " . $response_data['status'];
} else {
    // --- FAILURE: Hash mismatch! ---
    // Do NOT trust this data.
}

let isVerified = false;
if (remote_hash) {
    // Use crypto.timingSafeEqual for secure comparison
    try {
        const localHashBuffer = Buffer.from(local_hash, 'utf8');
        const remoteHashBuffer = Buffer.from(remote_hash, 'utf8');

        if (localHashBuffer.length === remoteHashBuffer.length) {
            isVerified = crypto.timingSafeEqual(localHashBuffer, remoteHashBuffer);
        }
    } catch (e) {
        // Error during buffer creation (e.g., bad hash)
        isVerified = false;
    }
}

if (isVerified) {
    // --- SUCCESS: Data is verified ---
    // console.log("Status:", responseData.status);
} else {
    // --- FAILURE: Hash mismatch! ---
}

import hmac

isVerified = False
if remote_hash:
    # Use hmac.compare_digest for secure comparison
    isVerified = hmac.compare_digest(local_hash, remote_hash)

if isVerified:
    # --- SUCCESS: Data is verified ---
    # print(f"Status: {response_data['status']}")
    pass
else:
    # --- FAILURE: Hash mismatch! ---
    pass

TRANSACTION STATUS :

Amount Mismatch : We received money but customer paid different money than the requested money
Approved : We received money same value as requested
Late Approved : We recieved money but it happened late while doing reconcilation from bank side
Declined : The transaction declined due to security reasons
Failed : The payment failed from bank side
Cancelled : This status for NonSeamess when customer cancel the payment from the screen
User Timed Out: The user did not complete the payment within the session period.

COMPLAINT

We have a dedicated Complaint Section where merchants can manage transaction-related complaints. Through this section, merchants can submit complaints with all necessary details and optional evidence. Upon submission, a unique complaint reference ID is generated, allowing merchants to track the complaint’s status and receive real-time updates via the status-check API. This ensures a smooth, secure, and efficient process for resolving any transaction issues.

Complaint

RECONCILIATION

This API endpoint allows authorized users to retrieve payment transactions based on a specific pid (Partner ID) and date. The API performs authentication using a token and signature verification to ensure secure communication.

Reconciliation

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