K Khay Dart & Flutter SDK 🎯

Official Dart and Flutter SDK for K Khay — The Non-Custodial Crypto Payment Gateway

Accept non-custodial cryptocurrency payments across 190+ blockchain networks and 500+ tokens (EVM, Bitcoin, Solana, TON, Tron, and XRPL) with zero custody and automatic direct-to-wallet settlement in Flutter mobile apps (iOS & Android), desktop apps, web apps, or backend Dart services.

Gateway Dashboard • API Keys • Website

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⚡ Highlights

• 🛡️ 100% Non-Custodial: Payments settle directly to your external wallet address in seconds. K Khay never holds your private keys or customer funds.
• 🌐 190+ Networks:
  • EVM (180+ Chains): BNB Smart Chain (bsc), Polygon (polygon), Base (base), Arbitrum (arbitrum), Ethereum (ethereum), Optimism (optimism), Avalanche (avalanche).
  • UTXO Chains: Bitcoin (bitcoin), Dogecoin (dogecoin), Litecoin (litecoin), Bitcoin Cash (bitcoincash).
  • High-Throughput Chains: Solana (solana), TON (ton), Tron (tron), XRP Ledger (ripple).
• 🪙 500+ Tokens: Native coins and tokens (USDT, USDC, BTC, ETH, SOL, TON, BNB, DOGE, XRP, TRX, LTC, DAI, and more).
• 📱 Flutter & Dart Native: Zero native platform dependencies, works smoothly across iOS, Android, macOS, Linux, Windows, and Web.
• 🔔 HMAC-SHA256 Webhook Engine: Timing-safe cryptographic signature validation (x-kkhay-signature).

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📦 Installation

Add kkhay to your pubspec.yaml:

dependencies:
  kkhay: ^1.0.4

Or run:

# In Flutter
flutter pub add kkhay

# In pure Dart
dart pub add kkhay

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🚀 Quickstart

1. Initialize the Client

Retrieve your API key from the K Khay Gateway Dashboard.

import 'package:kkhay/kkhay.dart';

final client = KkhayClient(
  apiKey: 'kkhay_live_your_api_key_here',
);

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2. Create a Crypto Payment Invoice

Accept stablecoins, native coins, or let the customer choose their chain on checkout:

// Example A: USDT on BNB Smart Chain (BSC)
final invoice = await client.createInvoice(CreateInvoiceRequest(
  amount: 49.99,
  currency: 'USD',
  payNetwork: 'bsc',        // 'bsc' | 'polygon' | 'base' | 'arbitrum' | 'ethereum' | 'solana' | 'bitcoin' | 'ton'
  payToken: 'USDT',         // 'USDT' | 'USDC' | 'BTC' | 'ETH' | 'SOL' | 'TON'
  orderId: 'ORDER-9842',    // Your internal order ID
  title: 'Annual Pro Plan',
  customerEmail: 'alice@example.com',
  redirectUrl: 'https://myshop.com/success',
));

print('Invoice ID: ${invoice.id}');
print('Gateway ID: ${invoice.gatewayId}');
print('Deposit Address: ${invoice.depositAddress}');
print('Checkout Hosted URL: ${invoice.hostedUrl}');

// In Flutter, open the hosted checkout in browser:
// launchUrl(Uri.parse(invoice.hostedUrl));

// Example B: Native Bitcoin or Solana
final btcInvoice = await client.createInvoice(CreateInvoiceRequest(
  amount: 120.00,
  currency: 'USD',
  payNetwork: 'bitcoin',
  payToken: 'BTC',
  orderId: 'ORDER-9843',
));

final solInvoice = await client.createInvoice(CreateInvoiceRequest(
  amount: 25.00,
  currency: 'USD',
  payNetwork: 'solana',
  payToken: 'SOL',
  orderId: 'ORDER-9844',
));

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3. Fetch & List Invoices

// Retrieve a single invoice with blockchain transaction history
final response = await client.getInvoice('01940000-0000-7000-8000-000000000001');

print('Status: ${response.invoice.status}'); // WAITING | PAID | EXPIRED | CANCELED
for (final payment in response.payments) {
  print('Received: ${payment.amountReceived} | Confirmations: ${payment.confirmations} | Tx: ${payment.txHash}');
}

// List recent invoices with pagination
final list = await client.listInvoices(
  page: 1,
  limit: 20,
  status: 'PAID',
);

print('Total Invoices: ${list.totalCount}');

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4. Verify Incoming Webhooks (IPN)

In your backend server (Shelf, Dart Frog, or serverless Dart), verify the incoming x-kkhay-signature header:

import 'package:kkhay/kkhay.dart';

void handleWebhook(String rawBody, String? signature, String webhookSecret) {
  try {
    final event = parseWebhookEvent(rawBody, signature, webhookSecret);

    if (event.event == 'payment.paid') {
      print('Payment confirmed for Order: ${event.orderId}');
      print('Tx Hash: ${event.txHash}');
      print('Amount: ${event.payAmount} ${event.payToken} on ${event.payNetwork}');
      // Fulfill your customer's order in your database
    }
  } on SignatureVerificationException catch (e) {
    print('Rejected invalid signature: $e');
  }
}

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5. Clean Resource Disposal

When your app or service is shutting down:

client.close();

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🌐 Supported Networks & Families

Network Family	Popular Chains	Supported Tokens
EVM (180+ Chains)	Ethereum, BNB Smart Chain, Polygon, Arbitrum, Base, Optimism, Avalanche	USDT, USDC, ETH, BNB, POL, AVAX, DAI, ERC-20s
UTXO	Bitcoin, Dogecoin, Litecoin, Bitcoin Cash	BTC, DOGE, LTC, BCH
Solana	Solana Mainnet	SOL, USDT, USDC
TON	The Open Network	TON, USDT
Tron (TVM)	Tron Mainnet	TRX, USDT
XRPL	XRP Ledger	XRP

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📄 License

MIT © K Khay