cryptocurrency-payment

name	Cryptocurrency Payment
description	Enabling direct peer-to-peer cryptocurrency transactions without intermediaries, including direct wallet payments, payment processors, transaction monitoring, and blockchain confirmation.

Cryptocurrency Payment

Current Level: Advanced
Domain: Blockchain / Payments

---

Overview

Cryptocurrency payments enable direct peer-to-peer transactions without intermediaries. This guide covers direct wallet payments, payment processors, and transaction monitoring for accepting crypto payments in applications.

Crypto Payment Concepts

Customer → Payment Request → Wallet → Blockchain → Confirmation → Order Complete

Payment Methods:

1. Direct Wallet - Customer sends crypto directly
2. Payment Processor - Third-party handles payments
3. Smart Contract - Automated payment handling

Direct Wallet Payments

// services/crypto-payment.service.ts
import { ethers } from 'ethers';

export class CryptoPaymentService {
  constructor(
    private provider: ethers.providers.Provider,
    private merchantAddress: string
  ) {}

  async createPaymentRequest(
    amount: string,
    currency: 'ETH' | 'USDC' | 'DAI'
  ): Promise<PaymentRequest> {
    const paymentId = this.generatePaymentId();
    const expiresAt = Date.now() + 15 * 60 * 1000; // 15 minutes

    return {
      paymentId,
      merchantAddress: this.merchantAddress,
      amount,
      currency,
      expiresAt,
      status: 'pending'
    };
  }

  async monitorPayment(
    paymentId: string,
    expectedAmount: string
  ): Promise<PaymentStatus> {
    const filter = {
      address: this.merchantAddress,
      topics: []
    };

    return new Promise((resolve) => {
      this.provider.on(filter, async (log) => {
        const tx = await this.provider.getTransaction(log.transactionHash);
        
        if (tx.to === this.merchantAddress) {
          const receivedAmount = ethers.utils.formatEther(tx.value);
          
          if (receivedAmount === expectedAmount) {
            resolve({
              paymentId,
              status: 'confirmed',
              transactionHash: tx.hash,
              amount: receivedAmount
            });
          }
        }
      });
    });
  }

  async verifyPayment(
    transactionHash: string,
    expectedAmount: string
  ): Promise<boolean> {
    const receipt = await this.provider.getTransactionReceipt(transactionHash);
    
    if (!receipt || receipt.status !== 1) {
      return false;
    }

    const tx = await this.provider.getTransaction(transactionHash);
    const receivedAmount = ethers.utils.formatEther(tx.value);

    return (
      tx.to === this.merchantAddress &&
      receivedAmount === expectedAmount &&
      receipt.confirmations >= 3
    );
  }

  private generatePaymentId(): string {
    return `pay_${Date.now()}_${Math.random().toString(36).substr(2, 9)}`;
  }
}

interface PaymentRequest {
  paymentId: string;
  merchantAddress: string;
  amount: string;
  currency: string;
  expiresAt: number;
  status: 'pending' | 'confirmed' | 'expired';
}

interface PaymentStatus {
  paymentId: string;
  status: string;
  transactionHash: string;
  amount: string;
}

Payment Processors

Coinbase Commerce

// services/coinbase-commerce.service.ts
import axios from 'axios';

export class CoinbaseCommerceService {
  private apiKey = process.env.COINBASE_COMMERCE_API_KEY!;
  private baseUrl = 'https://api.commerce.coinbase.com';

  async createCharge(data: CreateChargeDto): Promise<Charge> {
    const response = await axios.post(
      `${this.baseUrl}/charges`,
      {
        name: data.name,
        description: data.description,
        pricing_type: 'fixed_price',
        local_price: {
          amount: data.amount,
          currency: data.currency
        },
        metadata: data.metadata
      },
      {
        headers: {
          'X-CC-Api-Key': this.apiKey,
          'X-CC-Version': '2018-03-22'
        }
      }
    );

    return response.data.data;
  }

  async getCharge(chargeId: ): <> {
     response =  axios.(
      ,
      {
        : {
          : .,
          : 
        }
      }
    );

     response..;
  }

   (): <[]> {
     response =  axios.(
      ,
      {
        : {
          : .,
          : 
        }
      }
    );

     response..;
  }

  (: , : ):  {
     crypto = ();
     webhookSecret = process..!;

     expectedSignature = crypto
      .(, webhookSecret)
      .(payload)
      .();

     signature === expectedSignature;
  }
}

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NOWPayments

// services/nowpayments.service.ts
export class NOWPaymentsService {
  private apiKey = process.env.NOWPAYMENTS_API_KEY!;
  private baseUrl = 'https://api.nowpayments.io/v1';

  async createPayment(data: CreatePaymentDto): Promise<Payment> {
    const response = await axios.post(
      `${this.baseUrl}/payment`,
      {
        price_amount: data.amount,
        price_currency: data.currency,
        pay_currency: data.payCurrency,
        order_id: data.orderId,
        order_description: data.description,
        ipn_callback_url: data.callbackUrl
      },
      {
        headers: {
          'x-api-key': this.apiKey
        }
      }
    );

    return response.data;
  }

  async getPaymentStatus(paymentId: string): Promise<PaymentStatus> {
    const response = await axios.get(
      ,
      {
        : {
          : .
        }
      }
    );

     response.;
  }

   (): <[]> {
     response =  axios.(
      ,
      {
        : {
          : .
        }
      }
    );

     response..;
  }

   (
    : ,
    : ,
    : 
  ): <> {
     response =  axios.(
      ,
      {
        : {
          amount,
          : fromCurrency,
          : toCurrency
        },
        : {
          : .
        }
      }
    );

     response.;
  }
}

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Transaction Monitoring

// services/transaction-monitor.service.ts
export class TransactionMonitorService {
  private provider: ethers.providers.Provider;

  constructor(provider: ethers.providers.Provider) {
    this.provider = provider;
  }

  async waitForConfirmations(
    txHash: string,
    confirmations: number = 3
  ): Promise<ethers.providers.TransactionReceipt> {
    const receipt = await this.provider.waitForTransaction(txHash, confirmations);
    return receipt;
  }

  async getTransactionStatus(txHash: string): Promise<TransactionStatus> {
    const [tx, receipt] = await Promise.all([
      this.provider.getTransaction(txHash),
      this.provider.getTransactionReceipt(txHash)
    ]);

    if (!receipt) {
      return {
        : ,
        : 
      };
    }

     currentBlock =  ..();
     confirmations = currentBlock - receipt. + ;

     {
      : receipt. ===  ?  : ,
      confirmations,
      : receipt.,
      : receipt..()
    };
  }

  (
    : ,
    :  
  ):   {
     filter = {
      address,
      : []
    };

      =  () => {
       tx =  ..(log.);
       (tx. === address) {
        (tx);
      }
    };

    ..(filter, listener);

      {
      ..(filter, listener);
    };
  }
}

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Payment Confirmation

// services/payment-confirmation.service.ts
export class PaymentConfirmationService {
  async confirmPayment(
    transactionHash: string,
    expectedAmount: string,
    expectedRecipient: string
  ): Promise<ConfirmationResult> {
    const provider = new ethers.providers.InfuraProvider('mainnet');
    
    // Wait for confirmations
    const receipt = await provider.waitForTransaction(transactionHash, 3);

    if (receipt.status !== 1) {
      return {
        confirmed: false,
        reason: 'Transaction failed'
      };
    }

    // Verify transaction details
    const tx = await provider.getTransaction(transactionHash);

    if (tx.to?.toLowerCase() !== expectedRecipient.toLowerCase()) {
      return {
        confirmed: false,
        reason: 'Incorrect recipient'
      };
    }

    const receivedAmount = ethers.utils.formatEther(tx.);
     (receivedAmount !== expectedAmount) {
       {
        : ,
        : 
      };
    }

     {
      : ,
      transactionHash,
      : receivedAmount,
      : receipt.
    };
  }
}

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Multi-Currency Support

// services/multi-currency.service.ts
export class MultiCurrencyService {
  private supportedCurrencies = ['ETH', 'BTC', 'USDC', 'USDT', 'DAI'];

  async getExchangeRate(from: string, to: string): Promise<number> {
    // Use CoinGecko API
    const response = await fetch(
      `https://api.coingecko.com/api/v3/simple/price?ids=${from}&vs_currencies=${to}`
    );

    const data = await response.json();
    return data[from.toLowerCase()][to.toLowerCase()];
  }

  async convertAmount(
    amount: number,
    from: string,
    to: string
  ): Promise<number> {
    const rate = await this.getExchangeRate(from, to);
    return amount * rate;
  }

  async getPriceInCrypto(
    : ,
    : 
  ): <> {
     cryptoAmount =  .(usdAmount, , cryptocurrency);
     cryptoAmount.();
  }
}

Webhook Handling

// pages/api/webhooks/coinbase.ts
import type { NextApiRequest, NextApiResponse } from 'next';
import crypto from 'crypto';

export default async function handler(
  req: NextApiRequest,
  res: NextApiResponse
) {
  if (req.method !== 'POST') {
    return res.status(405).json({ error: 'Method not allowed' });
  }

  // Verify webhook signature
  const signature = req.headers['x-cc-webhook-signature'] as string;
  const payload = JSON.stringify(req.body);

  if (!verifySignature(signature, payload)) {
    return res.status(401).json({ error: 'Invalid signature' });
  }

  const event = req.body;

  // Handle different event types
  switch (event.) {
     :
       (event.);
      ;

     :
       (event.);
      ;

     :
       (event.);
      ;
  }

  res.({ :  });
}

 ():  {
   webhookSecret = process..!;
  
   expectedSignature = crypto
    .(, webhookSecret)
    .(payload)
    .();

   signature === expectedSignature;
}

  (): <> {
  
   db..({
    : { : data.. },
    : {
      : ,
      : data.[].
    }
  });

  
   emailService.(data..);
}

  (): <> {
   db..({
    : { : data.. },
    : { :  }
  });
}

  (): <> {
   db..({
    : { : data.. },
    : { :  }
  });
}

---

Quick Start

Payment Request

interface PaymentRequest {
  orderId: string
  amount: number  // in crypto (e.g., 0.01 ETH)
  currency: 'ETH' | 'BTC' | 'USDT'
  recipientAddress: string
}

async function createPaymentRequest(request: PaymentRequest) {
  const payment = await db.payments.create({
    data: {
      orderId: request.orderId,
      amount: request.amount,
      currency: request.currency,
      recipientAddress: request.recipientAddress,
      status: 'pending',
      expiresAt: addMinutes(new Date(), 15)  // 15 min expiry
    }
  })
  
  return {
    address: request.recipientAddress,
    amount: request.amount,
    currency: request.currency,
    qrCode: generateQRCode(`${request.currency}:${request.recipientAddress}?amount=`)
  }
}

Transaction Monitoring

async function monitorTransaction(txHash: string) {
  const provider = new ethers.providers.JsonRpcProvider(RPC_URL)
  
  // Wait for confirmations
  const receipt = await provider.waitForTransaction(txHash, 3)  // 3 confirmations
  
  if (receipt.status === 1) {
    await updatePaymentStatus(txHash, 'confirmed')
  } else {
    await updatePaymentStatus(txHash, 'failed')
  }
}

---

Production Checklist

• Wallet Integration: Support multiple wallets
• Payment Processing: Payment processor or direct wallet
• Transaction Monitoring: Monitor blockchain transactions
• Confirmations: Wait for multiple confirmations
• Amount Verification: Verify exact payment amount
• Address Verification: Verify recipient address
• Expiry: Payment request expiry
• Refunds: Refund process
• Security: Secure private keys
• Testing: Test on testnets first
• Compliance: Follow local regulations
• Documentation: Document payment flow

---

Anti-patterns

❌ Don't: No Confirmations

// ❌ Bad - Accept after 1 confirmation
const receipt = await provider.waitForTransaction(txHash, 1)
await completeOrder(orderId)  // Too risky!

// ✅ Good - Wait for multiple confirmations
const receipt = await provider.waitForTransaction(txHash, 3)  // 3 confirmations
await completeOrder(orderId)  // Safer

❌ Don't: Store Private Keys

// ❌ Bad - Store private keys
const wallet = new ethers.Wallet('0x...private-key...')  // Exposed!

// ✅ Good - Use payment processor
// Or hardware wallet
// Never store private keys in code

---

Integration Points

• Wallet Connection (35-blockchain-web3/wallet-connection/) - User wallets
• Smart Contracts (35-blockchain-web3/smart-contracts/) - Contract payments
• Payment Gateways (30-ecommerce/payment-gateways/) - Payment patterns

---

Further Reading

• Ethereum Payment Processing
• Bitcoin Payment Processing

Best Practices

1. Confirmations - Wait for multiple confirmations
2. Amount Verification - Verify exact payment amount
3. Address Verification - Verify recipient address
4. Webhook Security - Verify webhook signatures
5. Timeout Handling - Set payment expiration times
6. Multi-Currency - Support multiple cryptocurrencies
7. Price Updates - Update crypto prices regularly
8. Refunds - Implement refund mechanism
9. Testing - Test on testnets first
10. Compliance - Follow local regulations

Resources

• Coinbase Commerce
• NOWPayments
• BitPay
• CoinGecko API