Great question. You can validate “payment QR codes” at two levels:

1. Decode & structural checks (what you can do locally in code)
2. Live verification (needs a PSP/gateway API; optional but best-practice)

Below is a practical, copy-pasteable approach you can drop into your stack (PHP/Laravel, plus quick Node/Python snippets).

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1) What kinds of payment QR payloads you’ll see

• UPI intent URI (most common; including Paytm VPAs)
  Example:
  upi://pay?pa=merchant@paytm&pn=Acme+Store&am=123.45&cu=INR&tn=Order+123
• EMVCo / BharatQR TLV string (starts with digits)
  Example:
  000201010211...5303561540...6304ABCD (ends with CRC “63 04 XXXX”)
• Wallet/app-specific deep links
  • Paytm: upi://pay?... or paytmmp://... or short URL like https://paytm.me/...
    (Most Paytm merchant QRs are actually UPI with a Paytm VPA such as ...@paytm.)

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2) Flow to implement

A. Decode the QR image → get the raw text

• PHP: khanamiryan/qrcode-detector-decoder (ZXing port)
• Node: @zxing/library, jsqr
• Python: pyzbar or opencv + zbarlight

B. Decide the type & validate structurally

• If it starts with upi://pay → parse as URI, validate required params.
• If it looks like TLV (digits, starts with “00 02 01 02 11 …” etc.) → parse TLV and verify CRC16-CCITT in tag 63.
• If it’s app link (paytmmp:// or https://paytm.me/...) → allowlist the scheme/domain and (optionally) resolve server-side to ensure it’s a valid, reachable link owned by Paytm.

C. (Optional but recommended) Live verification

• You cannot guarantee a VPA exists or is active from the QR alone.
• Use a PSP/gateway that exposes VPA verification (aka “UPI PSP lookup”) APIs:
  • Razorpay, Cashfree, Paytm for Business, PhonePe, Juspay, etc.
  • Typically you send pa=merchant@bank to an endpoint → they reply if it’s valid and sometimes return the account holder name.

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3) Validation rules (UPI intent)

For upi://pay links:

• Scheme must be upi, host must be pay
• Required:
  • pa (VPA): ^[a-zA-Z0-9.\-_]{2,}@[a-zA-Z0-9.\-_]{2,}$
  • cu (currency): usually INR
• Common/optional: pn (payee name), am (amount), tn (note), tr (txn ref), tid, mc (merchant code), orgid, sign (signed intents)
• If you require fixed amount QRs, ensure am is present and numeric (^\d+(\.\d{1,2})?$).
• Reject unknown params if you want a strict policy, or allow a whitelist (pa,pn,am,tn,tr,tid,mc,cu,orgid,sign,mode).

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4) Validation rules (EMVCo/BharatQR TLV)

• TLV format: <TAG><LEN><VALUE> repeated, all numeric.
• CRC is tag 63 with length 04. Compute CRC16-CCITT (0x1021, init 0xFFFF) over the bytes up to but not including the CRC value, then compare with the provided 4-hex checksum.
• Presence of specific tags depends on the profile (UPI merchant, etc.). For basic acceptance, verifying a correct TLV structure + CRC already weeds out malformed codes.

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5) PHP (Laravel-friendly) samples

A) Decode the QR

composer require khanamiryan/qrcode-detector-decoder
Code language: JavaScript (javascript)

use Zxing\QrReader;

function decodeQrImage(string $path): ?string {
    $qrcode = new QrReader($path); // supports JPG/PNG, etc.
    $text = $qrcode->text();
    return $text !== '' ? $text : null;
}
Code language: PHP (php)

B) Validate UPI intent URI

function isValidUpiUri(string $s): bool {
    // quick precheck
    if (!str_starts_with($s, 'upi://pay')) return false;

    $parts = parse_url($s);
    if (($parts['scheme'] ?? '') !== 'upi') return false;
    if (($parts['host'] ?? '') !== 'pay') return false;

    parse_str($parts['query'] ?? '', $q);

    // Required fields
    if (empty($q['pa']) || empty($q['cu'])) return false;

    // VPA pattern (basic)
    if (!preg_match('/^[A-Za-z0-9._-]+@[A-Za-z0-9._-]+$/', $q['pa'])) return false;

    // Currency
    if (strtoupper($q['cu']) !== 'INR') return false;

    // Amount (if present)
    if (isset($q['am']) && !preg_match('/^\d+(\.\d{1,2})?$/', $q['am'])) return false;

    // Optional: enforce allowlist of params
    $allowed = ['pa','pn','am','tn','tr','tid','mc','cu','orgid','sign','mode'];
    foreach (array_keys($q) as $k) {
        if (!in_array($k, $allowed, true)) return false; // tighten as you prefer
    }

    return true;
}
Code language: PHP (php)

C) Detect & validate EMVCo/BharatQR TLV (CRC check)

function looksLikeTlv(string $s): bool {
    return ctype_digit($s) && strlen($s) >= 8; // rough heuristic
}

function parseTlv(string $s): array {
    $i = 0; $fields = [];
    while ($i + 4 <= strlen($s)) {
        $tag = substr($s, $i, 2); $i += 2;
        $len = intval(substr($s, $i, 2)); $i += 2;
        $val = substr($s, $i, $len); $i += $len;
        $fields[$tag] = $val;
        if ($i > strlen($s)) break;
    }
    return $fields;
}

// CRC16-CCITT (0x1021), init 0xFFFF, no xorout
function crc16_ccitt(string $data): string {
    $crc = 0xFFFF;
    $bytes = unpack('C*', $data);
    foreach ($bytes as $b) {
        $crc ^= ($b << 8);
        for ($i=0; $i<8; $i++) {
            $crc = ($crc & 0x8000) ? (($crc << 1) ^ 0x1021) : ($crc << 1);
            $crc &= 0xFFFF;
        }
    }
    return strtoupper(str_pad(dechex($crc), 4, '0', STR_PAD_LEFT));
}

function isValidEmvcoWithCrc(string $s): bool {
    if (!looksLikeTlv($s)) return false;
    // Find CRC tag "63"
    $pos = strpos($s, '63');
    if ($pos === false) return false;

    // The CRC field is "63 04 XXXX"
    $crcFieldStart = $pos;
    $dataForCrc = substr($s, 0, $crcFieldStart + 4); // include "63" + "04", exclude the 4 hex CRC value
    $providedCrc = substr($s, $crcFieldStart + 4, 4);
    // Compute CRC over the raw bytes, which here are ASCII digits; this simplified check is
    // acceptable for gating malformed QRs. For production, convert TLV to actual bytes.
    $calc = crc16_ccitt($dataForCrc);
    return strtoupper($providedCrc) === $calc;
}
Code language: PHP (php)

D) Putting it together

function validatePaymentQr(string $imagePath): array {
    $raw = decodeQrImage($imagePath);
    if ($raw === null) {
        return ['ok' => false, 'type' => null, 'reason' => 'QR not readable'];
    }

    // UPI intent?
    if (isValidUpiUri($raw)) {
        return ['ok' => true, 'type' => 'upi-intent', 'payload' => $raw];
    }

    // EMVCo TLV with valid CRC?
    if (looksLikeTlv($raw) && isValidEmvcoWithCrc($raw)) {
        return ['ok' => true, 'type' => 'emvco-tlv', 'payload' => $raw];
    }

    // Paytm deep links (allowlist)
    if (str_starts_with($raw, 'paytmmp://') || str_starts_with($raw, 'https://paytm.me/')) {
        return ['ok' => true, 'type' => 'paytm-link', 'payload' => $raw];
    }

    return ['ok' => false, 'type' => null, 'reason' => 'Unknown or malformed payment QR'];
}
Code language: PHP (php)

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6) Node & Python quickies

Node (decode + basic UPI check)

npm i @zxing/library
Code language: CSS (css)

const { BrowserQRCodeReader } = require('@zxing/library');

function isValidUpiUri(s) {
  try {
    const u = new URL(s);
    if (u.protocol !== 'upi:' || u.hostname !== 'pay') return false;
    const pa = u.searchParams.get('pa');
    const cu = u.searchParams.get('cu');
    if (!pa || !/^[A-Za-z0-9._-]+@[A-Za-z0-9._-]+$/.test(pa)) return false;
    if ((cu || '').toUpperCase() !== 'INR') return false;
    const am = u.searchParams.get('am');
    if (am && !/^\d+(\.\d{1,2})?$/.test(am)) return false;
    return true;
  } catch { return false; }
}
Code language: JavaScript (javascript)

Python (pyzbar)

pip install pyzbar pillow

from pyzbar.pyzbar import decode
from PIL import Image
from urllib.parse import urlparse, parse_qs

def is_valid_upi_uri(s: str) -> bool:
    try:
        u = urlparse(s)
        if u.scheme != 'upi' or u.netloc != 'pay': return False
        q = {k:v[0] for k,v in parse_qs(u.query).items()}
        pa = q.get('pa'); cu = (q.get('cu') or '').upper()
        if not pa or not cu: return False
        import re
        if not re.match(r'^[A-Za-z0-9._-]+@[A-Za-z0-9._-]+$', pa): return False
        if cu != 'INR': return False
        am = q.get('am')
        if am and not re.match(r'^\d+(\.\d{1,2})?$', am): return False
        return True
    except:
        return False

def decode_qr(path: str) -> str | None:
    d = decode(Image.open(path))
    return d[0].data.decode() if d else None
Code language: JavaScript (javascript)

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7) Security & product tips

• Don’t auto-trust a decoded string just because it parses. Enforce strict allowlists (schemes, hosts, param names).
• Sanitize & log the original payload for audit/debug.
• Optionally: if you only accept merchant (fixed-amount) QRs, reject those missing am.
• Live verification: integrate a PSP’s VPA validation API to confirm the VPA exists and is active before saving the QR to your database.
• Rate-limit and virus-scan uploads; store images in a safe bucket; validate mime & dimensions.
• UX: after upload, show the decoded details (VPA, name, amount) back to the user for confirmation.

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If you want something that is widely used in production and proven to work across banks, UPI apps, and wallets like Paytm, then the industry practice is:

✅ Most Widely Accepted Implementation

• UPI intent URI validation + (optionally) EMVCo TLV validation + VPA verification via PSP APIs.
• Almost all real-world QR codes in India today (Paytm, PhonePe, GPay, BHIM, BharatPe, banks) follow the NPCI UPI QR Standard which is based on EMVCo QR but typically presented as a upi://pay?... intent.
• So, in practice:
  1. Decode the QR → you’ll almost always get upi://pay?...
  2. Check required fields (pa, cu) + format (VPA regex, currency = INR)
  3. (Optional but best) Call a PSP/aggregator API to confirm the VPA is valid

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🚀 Why this is the standard

• Banks & UPI apps interoperate because NPCI mandated UPI intent URIs and EMVCo QR as the backbone.
• Paytm merchant QRs are just UPI QR with VPAs ending in @paytm.
• PhonePe, GPay, Amazon Pay, BHIM → all issue UPI QR codes in the same format.
• Even BharatQR (card+UPI) is EMVCo TLV under the hood, but most merchant-facing QRs still decode to a UPI intent.

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🔑 So in your system

• Implement UPI intent URI parsing & validation (like the PHP/Python snippets I showed).
• Treat Paytm links as a special-case allowlist (if you want to support their paytmmp:// or https://paytm.me/...).
• If you want bulletproof validation (to avoid fake VPAs), plug into a PSP’s VPA verification API (Razorpay, Paytm for Business, Cashfree, PhonePe, Juspay all provide it).

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👉 In short:
Decode QR → Validate UPI intent URI → (optional) Live VPA verification API.
That’s the widely accepted, real-world working approach used by payment apps and fintech companies.

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