Building a Crypto Payment Flow

If you’re building a digital product and want to accept cryptocurrency payments, the technical implementation is more straightforward than you might expect. Here’s a practical overview of how we built our crypto payment flow at CryptoeSIM.io and what we learned.

Choosing Your Integration Approach
You have two main options: use a payment processor (like BTCPay Server, CoinGate, or NOWPayments) or build a direct integration with blockchain nodes.

For most projects, a payment processor is the right starting point. It handles wallet management, transaction monitoring, currency conversion, and webhook notifications. BTCPay Server is the go-to open-source option — you host it yourself and there are no intermediary fees. Hosted solutions like CoinGate are simpler to set up but charge a small
percentage.

The Basic Flow
A typical crypto checkout flow works like this:

1. Customer selects a product and chooses crypto payment

2. Your backend calls the payment processor API to create an invoice

3. The processor returns a payment address and amount (converted from your base
   currency to the requested crypto at current rates)

4. Your frontend displays this as a QR code and/or copyable address

5. Customer sends crypto from their wallet

6. The processor monitors the blockchain for the incoming transaction

7. After sufficient confirmations, the processor sends a webhook to your backend

8. Your backend fulfils the order

For digital products with instant delivery, you’ll want to decide how many confirmations
to require. Zero-confirmation (accepting the transaction as soon as it appears in the
mempool) is risky due to potential double-spend attacks. One confirmation is often sufficient for low-value digital goods. Three to six confirmations is standard for higher-value
transactions.

Handling Multiple Cryptocurrencies
Supporting Bitcoin, Ethereum, and stablecoins means handling different blockchain architectures. Payment processors abstract most of this complexity. If building direct integrations, you’ll need separate node infrastructure for each blockchain.

Stablecoins (USDT, USDC) are worth prioritising because they eliminate exchange rate
volatility. A $10 product costs exactly $10 in USDT, simplifying accounting and refund
handling.

Practical Considerations
Set invoice expiry times. Crypto prices fluctuate, so the quoted exchange rate should
only be valid for a limited window (typically 15–30 minutes). If the customer doesn’t pay in time, generate a new invoice with updated rates. Handle underpayments and overpayments gracefully. Network fees can cause the received amount to be slightly less than expected. Build tolerance into your validation logic or provide clear instructions about including network fees.

Webhook security is critical. Verify webhook signatures from your payment processor.
Never trust client-side payment confirmations.

Settlement
Decide whether to hold crypto or convert to fiat. BTCPay Server lets you hold received crypto. Hosted processors can auto-convert to fiat and deposit to your bank account. Many businesses do a mix of both.

Building a crypto payment flow for digital products is a manageable engineering project. The tooling has matured significantly, and for digital products with instant delivery, it creates a fast, global payment option that your customers will appreciate.