A crypto checkout with no backend: verifying a USDT payment from the browser

Most e-commerce checkouts require a heavy stack: a database to store orders, a server to handle logic, and a way to listen to blockchain events.

But what if you could build a fully functional service store using only a static site?

In this article, I’ll walk through how the crypto-store handles payments. We aren't using a traditional backend to watch for transaction events. Instead, we use a "balance-delta" method—verifying a USDT (BEP-20) payment directly from the visitor's browser using a public RPC.

The Architecture: No Backend, No Problem

When a user visits the store to order a service (like an AI code review or a landing page), the site needs to know if they actually sent the money. Usually, this requires a backend to index blockchain events.

Instead, we use a Client-Side Balance Check. Here is the logic:

1. The Baseline: When the user initiates an order, the app performs an eth_call to get the current USDT balance of the store's wallet.
2. The Watchdog (Polling): Once the baseline is set, the browser doesn't just sit idle. It initiates a polling loop. Every 20 seconds, the app sends a new eth_call using the balanceOf selector (0x70a08231) to check the current USDT balance of the store's wallet.
3. The Verification: The app calculates the difference between the new balance and the baseline. If that difference is greater than or equal to the quoted amount—with a 0.1% tolerance to account for any minor rounding or precision issues—the payment is flagged as "Paid" in the browser.
4. The TTL (Time-to-Live): To prevent the app from waiting indefinitely, the check expires after 60 minutes. If the payment isn't detected within this window, the session expires.

The "Honesty" Disclaimer: Why this isn't a perfect automated system

While this method is incredibly efficient for a static site, it isn't without its quirks. Because we are using a "balance-delta" check (looking at how much the total wallet balance increased) rather than looking for a specific transaction hash, there are two things you should know:

1. The Concurrent Buyer Risk: If two people pay at the exact same moment, the app might see a single large jump in the wallet balance and attribute it incorrectly. This is a known technical limitation of using a single wallet for multiple simultaneous orders.
2. The Human-in-the-Loop: Because of the reason above, the "Paid" status in your browser is a convenience, not a final legal contract. To ensure 100% accuracy, the owner manually verifies every transaction on BscScan before beginning any work.

Delivery & Refunds

Because this is a service-based store (offering things like AI code reviews and landing page builds), the process isn't instant:

• Delivery: Once your payment is confirmed, your service will be delivered via email or Telegram within 24-48 hours.
• Refunds: All sales are final. There are no refunds, so please ensure you are sending USDT on the BNB Smart Chain (BEP-20). Sending USDT on any other network (like Ethereum or Polygon) will result in lost funds.

If you want to see this logic in action, or if you need a resume rebuild, a landing page, or a deep-dive AI code review, head over to the crypto-store.

Disclaimer: This article was written with AI assistance.