Crypto Payment Gateway: How Modern Payment Systems Actually Work

Intro — what this guide covers

Suppose you need a crypto payment gateway that helps you accept crypto payments without rebuilding checkout. This article shows how it works across chains, how to keep status updated, and how a white-label setup lets you control policy, branding, and settlement.

Two approaches

There are two main ways to accept crypto payments — directly or through a crypto payment gateway. Each has its own features.

Accepting crypto payments directly

Relevant if you have a small number of transactions or work with regular clients. To accept cryptocurrency directly, you need to:

• Create a crypto wallet (for example, in USDT or BTC).
• Share the wallet address with the client.
• Receive the funds and verify the transaction.
• Manually record the transaction details for accounting.
• Exchange or move the crypto yourself.

All tracking and reporting is done manually. As the number of transactions or clients grows, the workload increases — along with the risk of errors.

Payment gateway: automation and structure

A crypto payment gateway handles the entire payment process for you. It shows customers how much to pay, accepts the payment, and notifies you when it’s completed.

This step-by-step flow shows how to accept cryptocurrency payments:

1. A customer selects a product/plan.
   The system creates an invoice and issues an address (HD-wallet) on the required network. The address can be created for every user (and all subsequent invoices for this specific user will have previously created address) or taken from a rotating pool — it depends on your unit economics and the volume of micropayments. There’s a payment TTL (Time-to-Live). A partial payment can extend the TTL until the full amount is covered.
   
   
2. The customer pays.
   
   
3. Indexer watches the chain and emits events.
   It reads new blocks via RPC, decodes the fields that matter, and streams events into the bus (e.g., NATS JetStream). The core service listens to this stream.
   
   
4. Transfer Handler matches payment to invoice.
   It reconciles the incoming transfer with the internal invoice, writes the new state to the database (Postgres), and publishes an update. The frontend subscribes via SSE so the status updates in real time.
   
   
5. Notifications fire by policy.
   Bot/email alerts trigger according to rules — for manual sweeping or for automatic cash-in alike.
   
   
6. Sweeping / consolidation to treasury.
   Funds from many addresses are collected into your main wallet. This can be an offline utility on your laptop or an automated function (e.g., AWS Lambda) triggered by notifications. The private key is required only on the sweeping side; the core stores public keys only.

How Crypto Payment Gateways Work Across Multiple Chains

Let’s break down a much more detailed walkthrough of the specific crypto payment gateway by Rock’n’Block.

Part I — Indexer Core

The Indexer Core is developed to turn raw blocks from multiple chains into a clean, unified stream of payment events. That stream drives invoice state in the app and triggers status updates.

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Chain RPC (CHAIN#1/2/3 RPC)

The RPC layer is only the data source, but it matters operationally: requests are rate-limited, endpoints are duplicated, and health checks decide which node feeds a given poller so temporary outages don’t become incidents.

• Input: RPC nodes of a specific network (BTC/ETH, any EVM, etc.).
• What it does: data source for pollers. Duplicates RPC endpoints and rate-limits requests to avoid throttling and downtime.
• Output: blocks and transaction logs.

Chain Poller (CHAIN#1/2/3 POLLER)

The poller reads blocks strictly by height and keeps a crash-safe checkpoint in Redis, allowing predictable forward progress, quick restarts, and doesn’t flood the downstream services when traffic spikes. 

• Input: the network’s RPC.
• What it does: walks new blocks sequentially using a pointer to the last processed block (stored in Redis). On RPC hiccups it retries with backoff.
• Output: a stream of raw blocks to the decoder for its chain.

Chain Decoder (CHAIN#1/2/3 DECODER)

Raw blocks go to the Chain Decoder, a lightweight component that extracts only payment-relevant data and discards the rest. The decoder turns chain-specific structures into a single schema:

{ chain, currency, amount, from, to, timestamp, block, txHash }.

• Input: raw blocks/logs from the poller.
• What it does: extracts payment-relevant facts and normalizes them to a single schema. Per-chain/token rules (transfer events, inbound address, etc.) apply. On reorgs it emits correction events.
• Output: compact, normalized events.

NATS JetStream (NATS JS)

Normalized events flow into NATS JetStream — a durable event log with subjects per chain or asset, consumer groups, and server-side offset tracking. This gives us two critical properties:

• Back-pressure: bursts of on-chain activity are absorbed by the broker, so the pollers don’t have to slow down just because a downstream service is doing maintenance.
• Replay: after fixing a bug or deploying a new consumer, we can rewind a specific window of events and rebuild state without re-indexing.

Note: scanners/decoders can run on separate instances. The system push only payment-relevant data: chain, asset, amount, from/to, block/tx

• Input: normalized events from decoders (subjects per chain/asset).
• What it does: durable delivery, durable consumers, offset tracking, replay for recovery; natural back-pressure buffer for spikes.
• Output: a reliable event stream for the Invoices App.

Part II — Invoices App

Exposes a REST API for synchronous operations and SSE (Server-Sent Events) for real-time status to browsers and dashboards. The service picks an address, returns it with a TTL (Time-to-Live) that locks the quote for a short payment window, and immediately opens an SSE stream so the UI can render payment details and a countdown for a consumer.  

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Purpose: issue invoices, keep their state updated, show live progress, send secure notifications to your backend, and manage TTL (expiration).

REST API + SSE

• Input: requests from the Client Management Proxy.
  
  
• What it does: invoice CRUD (Create, Read, Update, Delete) and real-time status via SSE:
  
  • Create invoice — amount/asset/network/addressing model → returns address and TTL.
  • Check invoice by ID — synchronous status (for back office/admin).
  • Subscribe to invoice status via SSE — browser gets created → pending → confirmed → paid (and specials: expired, underpaid, overpaid) without polling.
  • Increase invoice TTL — extend the payment window per policy (partials can extend TTL).
  • Mark invoice as completed — administrative override if you accept payment manually (rare but possible).

• Output: sync responses and a long-lived SSE stream to the browser.

Queue Processor

When an invoice’s TTL expires, the queue changes state to expired, emits updates to subscribers, and, if configured, schedules a refresh flow that lets the buyer request a new quote in one click. If a customer sends a small “test” amount before the term closes, the same queue can extend the TTL automatically according to your rules. The customer can send the rest without creating a new invoice.

Transfer Handler

Subscribes to JetStream and matches inbound transfers to invoices by network, address (and tag/memo where relevant), and known context.

When the handler sees a relevant event, it writes an immutable payment record to Postgres, advances the invoice state (created → pending → confirmed → paid), calculates underpaid or overpaid exceptions when totals don’t match the quote, and publishes the new status to the open SSE stream so the buyer’s page updates in real time. If the decoder later emits a reorg correction, the handler reverts the invoice to pending and then promotes it again after sufficient confirmations.

• Input: events from NATS JetStream.
• What it does: matches inbound transfers to invoices, records the tranche in the DB, moves state, computes under/overpayments, publishes UI updates over SSE, and triggers webhooks. Handles reorg corrections.
• Output: Postgres writes + UI events + external notifications.

Postgres

All transitions land in Postgres. Whenever an invoice crosses a meaningful boundary (e.g., reaches finality), the app triggers webhooks to your backend. This is when you flip an order to paid, ship goods, grant entitlements, or book a ledger entry. Signatures and idempotency rules make handlers safe to retry: if a webhook arrives twice, your system doesn’t fulfill twice.

TG API (notifications)

Notifications service that forwards ops-level alerts to a channel or bot — large payments, error spikes, or missing RPC status—and, if needed, triggers the settlement workflow.

Client Management Proxy

A multi-tenant gateway that lets several sites or widgets share one payment core without copy-pasting the same logic into every app. It’s especially useful when you run multiple brands or regions and want one solution.

Addresses: two models that cover most real-world traffic

You can issue a fresh HD address per user or get it from a rotation pool:

• A unique address per user gives clean analytics and easy matching, but on chains with high fees, it can be costly to sweep every small balance (e.g., Marketplaces, booking, licence delivery).
• A rotation pool reduces sweeping costs in bursty workloads, but you must design the UX to avoid people paying to “old” addresses and you should set rational minimums like CEXs do, since dust can be uneconomical to move (e.g., apps with reusable in-app balances).

The point is choice: the core supports both models, and your business logic controls which one applies.

Settlement and sweep: keep keys where they belong

Funds land on many addresses. Finance wants them in one place. That sweep step is where you sign outbound transactions, so it’s where the private keys live. 

The safe pattern is simple: 

• The core holds only public keys and derives HD addresses for invoices. 
• Private keys belong to a separate sweep process that you control, which can be strictly offline, semi-automated with human approval, or fully automated on a short-lived worker (e.g., AWS Lambda) that wakes up, signs, and disappears. 

Integrating Blockchain Cryptocurrency Payment Solutions on Your Website

Integration is common: one API call to create invoices, one SSE subscription for status. The modal shows payment details, countdown, and retry logic. Back office gets webhooks and maps paid, expired, underpaid to familiar order states. That’s integrating cryptocurrency payment solutions on your website without rebuilding checkout.

How do businesses accept crypto payments online via checkout flows?

A business integrates crypto like any other processor: 

• When a buyer picks “Pay with crypto,” the backend creates an invoice/charge, and the gateway pushes status changes (pending → confirmed) to you via signed webhooks for automatic fulfillment.
  
  
• Invoice lifecycles include clear states and exception handling (e.g., underpaid/overpaid) with documented refund paths, giving support and finance a single, auditable flow.
  
  
• The page reflects progress, and the backend flips the order to paid the moment confirmations land — no manual checks, no rebuild of your current checkout.

Edge cases that separate a demo from a real processor

Real traffic is messy. People overpay or underpay. Chains slow down. Your crypto payment gateway should treat these not as “gotchas,” but as normal states.

• “Underpay” becomes a state with a clear policy: accept as paid, request a top-up, or refund, and log the action. 
• “Overpay” gets the same treatment, with a partial refund or a credit. 
• If a chain is congested, your TTL policy allows creation of a new quote automatically. 
• Any invoice is marked "paid" only after chain finality + N confirmations. 

White-label solution integration benefits

A white-label crypto payment gateway gives you control over branding, policy, and change velocity. You can add chains, tune confirmation rules, change TTLs, and update sweep thresholds. And because the core is modular, you can put your risk controls where they matter, like auto-swap rules on confirm.

Business opportunities

Benefits of using a ready-made crypto payment solution:

• Faster time-to-market + specialist talent. Outsourcing lets you tap a team that already ships multi-chain payments, event streams, and webhook workflows—so you go live sooner and avoid the in-house learning curve. Recent surveys show speed, agility, and access to skilled talent are now primary reasons companies outsource, not just cost.
  
  
• Lower total and opportunity cost. You convert months of hiring and ramp-up into a scoped delivery, often at lower blended rates. Meanwhile, your core team stays focused on the product that makes money.
  
  
• Scalability, brand control, and global reach. White-label payments keep your UX under your logo, while the platform scales across spikes and new markets. This is a core advantage called out in industry write-ups on white-label payment platforms.
  
  
• Flexible settlement choices. A well-implemented crypto gateway can settle to fiat, stablecoins, or a mix, so finance chooses risk exposure per market without changing checkout.
  
  
• Clear SLAs and accountability. Modern outsourcing relationships are increasingly outcome-based, with explicit service levels around delivery, uptime, and incident response — aligning the studio’s incentives with your business KPIs.

FAQ

How does a crypto payment gateway work?
It creates invoices, shows a checkout page, detects incoming transfers, waits for confirmations, updates status to paid, and notifies your backend so orders move without manual hacks.

How do payment gateways and processors work together?
The gateway supports checkout and status; the processor (network + settlement) moves funds and signals finality. They stay consistent via signed callbacks and idempotent writes.

How to accept crypto payments online on my website?
Add a crypto method in checkout, create invoices through the backend, show a QR and timer, subscribe to SSE for live status, act on webhooks, reconcile like any other method.

How do businesses integrate crypto payments into checkout flows?
They enable crypto behind a feature flag, map invoice states to existing order states, reuse refund logic, and tune confirmations per chain so crypto behaves like a standard processor.

How to create a crypto payment gateway?
Build chain watchers, a durable stream, an invoice service with explicit states, a Postgres ledger, SSE for UIs, and signed webhooks; keep private keys in a separate sweep.

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