Add UPI Checkout to Any Website, App & Software

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LION UPI PAYMENT GATEWAY — UNIVERSAL AI INTEGRATION MASTER PROMPT
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You are an expert full-stack engineer and payment integration specialist.
Your task is to integrate the Lion UPI Payment Gateway into my current project cleanly, safely, and without breaking, deleting, or modifying any existing functionality, routes, UI styles, database schemas, or business logic.

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1. MY GATEWAY CREDENTIALS & API ENDPOINTS
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• Gateway Name: MTG Pay (Universal UPI Gateway)
• Base API URL: https://mail.printin.space/api
• Create Order Endpoint: POST https://mail.printin.space/api/create-order
• Check Status Endpoint: POST https://mail.printin.space/api/check-status
• Payment Page Format: https://mail.printin.space/pay/{token}
• Mode: Production (0% Gateway Commission, Instant T+0 Peer-to-Bank Settlement)

My Production Credentials:
• API Key (X-API-Key): pi_live_sample_key_99812903
• API Secret (X-API-Secret): sk_live_sample_secret_74829104

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2. CRITICAL ZERO-HARM INTEGRATION RULES (DO NOT BREAK MY PROJECT)
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1. ANALYZE FIRST: Inspect my existing codebase structure, framework (e.g. Next.js, React, Node/Express, PHP/Laravel, WordPress/WooCommerce, Python/Django/Flask, Flutter, React Native, Android Kotlin, iOS Swift, C# .NET, Java, or HTML/JS), router, database models, and existing checkout/cart flow.
2. ZERO HARM: Do NOT delete, rewrite, or break any existing code, routes, tables, or design systems. Only append or integrate the necessary payment initiation and verification hooks.
3. SECURITY FIRST: Never expose `X-API-Secret` in frontend client-side bundles or public JavaScript. Store credentials in server-side environment variables (.env as LION_UPI_API_KEY and LION_UPI_API_SECRET) or server config.
4. MATCH MY DESIGN: Any checkout button, modal, or status confirmation screen you create must seamlessly match my project's existing UI, CSS framework (Tailwind, Bootstrap, styled-components, or custom CSS), and font styling.

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3. STEP-BY-STEP IMPLEMENTATION SPECIFICATION
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STEP 1: INITIATE PAYMENT ORDER (SERVER-SIDE)
When the customer clicks 'Pay' or 'Checkout', create a server-side POST request to:
POST https://mail.printin.space/api/create-order

Required Headers:
  Content-Type: application/json
  X-API-Key: pi_live_sample_key_99812903
  X-API-Secret: sk_live_sample_secret_74829104

JSON Request Body:
{
  "amount": <order_amount_in_inr_as_number_or_float>,
  "order_id": "<unique_order_id_string_from_my_database>",
  "customer_name": "<buyer_name>",
  "customer_mobile": "<buyer_10_digit_mobile_optional>",
  "callback_url": "<my_app_return_callback_url>",
  "description": "<order_description_or_product_name>"
}

Success Response (HTTP 201):
{
  "status": "success",
  "message": "Order created successfully",
  "data": {
    "payment_url": "https://mail.printin.space/pay/TOKEN_XXXXXX",
    "order_id": "<order_id>",
    "token": "TOKEN_XXXXXX",
    "amount": 499.00,
    "currency": "INR"
  }
}

Action: Redirect the customer to `data.payment_url` (or open via native UPI Intent / Deep-Link / in-app WebView for mobile apps).

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STEP 2: PAYMENT STATUS VERIFICATION (ON RETURN CALLBACK)
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When the customer finishes payment, the gateway redirects them back to:
<my_app_callback_url>?order_id=<order_id>&status=<status>

Do NOT trust frontend query parameters alone. Always verify securely from your server by calling:
POST https://mail.printin.space/api/check-status

Headers:
  Content-Type: application/json
  X-API-Key: pi_live_sample_key_99812903
  X-API-Secret: sk_live_sample_secret_74829104

JSON Body:
{
  "order_id": "<order_id>"
}

Response (HTTP 200):
{
  "status": "success",
  "data": {
    "order_id": "<order_id>",
    "status": "success",          // Possible values: 'success', 'pending', 'failed'
    "amount": 499.00,
    "utr": "425983742918",        // Bank UPI UTR Reference Number
    "payment_method": "UPI",
    "paid_at": "2026-09-18 12:00:00"
  }
}

Action:
• If data.status === 'success', update the order status in my database to 'PAID', store the bank utr, and display the confirmation receipt.
• If pending or failed, show an appropriate friendly message and allow the customer to retry.

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STEP 3: WEBHOOK RECONCILIATION (OPTIONAL BUT RECOMMENDED)
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Set up a webhook endpoint (e.g. /api/webhooks/lion-upi):
1. Read raw JSON body.
2. Read header X-PayIndia-Signature.
3. Compute HMAC-SHA256 of raw body using API Secret:
   expected_sig = hmac_sha256(raw_body, "sk_live_sample_secret_74829104")
4. If signature matches and event === 'payment.success', update order status to PAID in background.

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4. HOW YOU SHOULD PROCEED NOW
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1. First, tell me what framework/stack you detected in my project.
2. Show the proposed file additions (e.g. .env additions, backend controller/route, and checkout button hook).
3. Ensure no existing feature is broken.
4. Implement the integration cleanly and verify syntax.