Custom Crypto Payment Gateway Development & Integration

We often hear from clients: "We want to accept cryptocurrency on our website like a regular Stripe, but without intermediaries." It seems straightforward — just hook up a blockchain listener and generate addresses. But in production, problems emerge: detecting payments without constant polling, volatility during conversion, partial payments, confirmation thresholds in different networks, and idempotency during failures. We tackle volatility by fixing the exchange rate through Chainlink Price Feed. We've broken down each of these issues in production and offer a turnkey architecture. Our team has over 5 years of blockchain development experience and has implemented over 20 payment gateway integrations, processing over $10M in crypto transactions. Savings from eliminating intermediaries can reach 2% of turnover (average $20,000 per year for a $1M annual volume). Contact us for a consultation to evaluate your project.

How a Crypto Payment Gateway Works

A minimal viable payment gateway consists of four components:

[Client] → [API Gateway] → [Payment Service]
                                  ↓
                        [Blockchain Listener]
                                  ↓
                        [Event Queue (Redis/Kafka)]
                                  ↓
                        [Settlement Service] → [ERP/CRM]

Payment Service — creates an order, generates a unique address (or payment ID), and returns payment data to the client. Stateful — stores a mapping address → order. Blockchain Listener — monitors incoming transactions. This is the most critical component for reliability. Two approaches:

1. WebSocket subscription (eth_subscribe("logs", filter) or eth_subscribe("newHeads")) — low latency (10x faster than polling), but connections break; needs reconnect with backoff and replay of missed blocks.
2. Polling + cursor — less elegant but predictable. Store the last processed block, poll eth_getLogs with a filter by addresses. More resilient to network failures.

For production: a hybrid approach — WebSocket for low latency, polling as a fallback with cursor-based recovery.

Event Queue — a buffer between listener and settlement. Kafka for high loads, Redis Streams for medium loads. Key point: the listener publishes a TransactionDetected event, the settlement service subscribes. This decouples components and guarantees processing even if the settlement service temporarily goes down.

Settlement Service — checks confirmations, converts amounts, updates order status, and notifies the upstream system (webhook).

Why Custom Crypto Payment Gateway Detection Is the Hardest Component

EVM Networks (ETH, BNB, Polygon, Arbitrum, ...) and EVM Transaction Detection

Native ETH transfers: monitor via eth_subscribe("newHeads") + eth_getBlockByNumber and filter transactions by to address.

ERC-20 tokens (USDT, USDC, DAI): monitor the Transfer(address indexed from, address indexed to, uint256 value) event via eth_getLogs with a filter:

const filter = {
  fromBlock: 'latest',
  topics: [
    ethers.id('Transfer(address,address,uint256)'),
    null, // from: any
    ethers.zeroPadValue(paymentAddress, 32), // to: our address
  ],
};

Important for USDT (Tether): it has a non-standard ERC-20 — the transfer function does not return a bool. Calling through the standard interface will revert. Use safeTransfer or a low-level call with return data check.

Bitcoin Payment Gateway and UTXO Model

For BTC there is no "address → transaction" concept at the node level. Use either:

• Electrum Server (Electrs) — indexes UTXOs by addresses, allows subscription to an address
• BlockCypher / Blockcypher WebHook API — hosted solution but third-party dependency
• Bitcoin Core with importaddress — add the address to the wallet node, receive notifications via ZMQ

Minimum confirmations for BTC: 1 for small amounts (<$100), 3 for medium, 6 for large. For Ethereum, 12–20 blocks are sufficient.

TON Payment

TON transactions are asynchronous: an incoming transfer is a bounce-able message, and you must verify it is a transfer and not a bounce. Use TonAPI or TON Center API with a webhook on the address.

How to Ensure Webhook Idempotency (100% Idempotency Guarantee)

Notifications to the upstream system via webhook must be idempotent — duplicate deliveries on retry are possible. Include payment_id (unique) + tx_hash + status in the payload. The upstream system must check if it has already processed that payment_id. Retry policy: exponential backoff, 5–10 attempts, then a dead letter queue for manual inspection.

Confirmation Threshold and Double-Spend Protection

Never consider a payment completed after first detecting a transaction in the mempool — that is a pending state, not confirmed. Minimum thresholds:

Partial Payments and Overpayments

Real users sometimes pay the wrong amount — exchanges deduct fees, people make mistakes. A policy is needed:

• Underpayment: if 99–100% of amount received — treat as paid (1% tolerance). If less — partially_paid, wait 30 minutes for top-up, then expired.
• Overpayment: automatically accept, refund the difference (requires a refund flow) or credit as a credit note.

Comparison of Detection Approaches

# config.yml
listener:
  networks:
    - name: ethereum
      rpc: wss://eth-mainnet.g.alchemy.com/v2/YOUR_API_KEY
      polling_interval: 12s
      confirmations: 12
      addresses:
        - 0xYourPaymentAddress
    - name: bitcoin
      rpc: http://user:pass@localhost:18332
      confirmations: 3
      addresses:
        - bc1q...
    - name: polygon
      rpc: wss://polygon-mainnet.infura.io/ws/v3/YOUR_KEY
      confirmations: 128
      addresses:
        - 0x...

Tech Stack for Crypto Payment Integration

• Node.js + TypeScript or Go for listeners and API — good web3 library support
• ethers.js v6 or viem for EVM interaction
• PostgreSQL for payment storage (ACID, transactional status updates)
• Redis for rate limiting and rate caching
• Kafka or Redis Streams for event queue
• Grafana + Prometheus for monitoring: listener lag vs chain head, processing speed, errors

A custom gateway makes sense for volumes >500 payments/day or when specific requirements for privacy and control exist. For smaller volumes, NOWPayments, CoinGate, or similar cover the need more cheaply.

How to Set Up a Listener: Step-by-Step Guide for Crypto Payment API

1. Choose a network and determine the required confirmation threshold.
2. Deploy a WebSocket or polling listener with reconnection.
3. Set up a filter by addresses via eth_getLogs for tokens or by to for native coins.
4. Connect an Event Queue (Redis Streams for medium loads).
5. Implement a Settlement Service with idempotency checks.
6. Test on a testnet by simulating partial and double-spend payments.

What's Included in Custom Payment Gateway Development Work

• API gateway documentation in OpenAPI format
• Source code repository (GitLab/GitHub) with a usage license
• Deployment to your infrastructure or cloud
• Team training (2-hour workshop)
• Technical support for 30 days after launch
• Comprehensive crypto acquiring capabilities

Investment in development pays off through reduced fees and full control over the payment flow. Get a free engineering consultation — we'll help you decide on the architecture. Contact us to evaluate your project.

Blockchain Infrastructure Deployment: Nodes, RPC, Indexing

Subgraph fell at 3:47 AM. By morning users saw outdated balances, transactions "hung" in the UI, support received 47 tickets in an hour. Cause: the handler in the subgraph failed on a transaction with a non-standard event log — and the entire index stopped. We have encountered such situations dozens of times. Our experience shows: blockchain infrastructure does not forgive gaps in observability. Guaranteeing uptime without multi-layered monitoring and fault-tolerant architecture is impossible. Over 8 years working with Ethereum, Polygon, and Solana, we have developed an approach that allows predictable deployment of infrastructure of any scale — from a single node to a multichain grid with dozens of subgraphs.

RPC Layer Architecture

Every dApp interaction with the blockchain goes through RPC — the JSON-RPC API provided by a node. Three options:

Managed providers — Alchemy, QuickNode, Infura, Ankr. Minimal operational costs, SLA, built-in monitoring. Limits: rate limits (Alchemy Free: 300 RU/sec), vendor lock, potential downtime during provider incidents. For most projects — the right choice at the start.

Self-owned nodes — full control, no rate limits, no third-party dependence. Cost: archive Ethereum node requires 2.5–3TB SSD, a strong server, and DevOps support. Sync from scratch on Ethereum via Geth/Nethermind — 3–7 days. Justified under high load or latency requirements.

Hybrid — self-owned node as primary, managed provider as fallback. Standard for protocols with high TVL. Proper load balancing can reduce costs by 20–30% compared to pure managed setup. Under high monthly request volume, hybrid saves significantly.

How to Set Up an RPC Layer Without a Single Point of Failure?

At least two providers, DNS round-robin with health check every 5 seconds, automatic fallback when latency >500 ms. In practice, this gives 99.99% availability during any provider failure. For protocols with high TVL, we recommend a custom HA-proxy (nginx or Envoy) in front of two managed providers.

Why Is a Hybrid RPC Scheme More Cost-Effective Than Pure Managed?

At high request volumes, managed providers can be very expensive; a hybrid using a self-owned node as primary and a managed fallback cuts costs significantly without losing SLA.

Ethereum Node Clients

Execution clients: Geth (most used), Nethermind (C#, fast sync), Besu (Java, enterprise), Erigon (fastest sync, efficient archive mode ~2TB instead of 3TB).

Consensus clients (post-Merge): Lighthouse (Rust), Prysm (Go), Teku (Java), Nimbus (Nim). Each node after The Merge requires a pair of execution + consensus clients.

For DevOps: eth-docker — Docker Compose configurations for all client combinations. Setting up monitoring via Grafana + Prometheus is mandatory; a standard dashboard is available in each client's repository.

The Graph: Event Indexing

The Graph Protocol — decentralized indexing. A subgraph describes which events from which contracts to index and how to transform them into a GraphQL schema.

Subgraph structure:

• subgraph.yaml — manifest: contract addresses, startBlock, events to handle
• schema.graphql — GraphQL schema of entities
• src/mapping.ts — AssemblyScript event handlers

dataSources:
  - kind: ethereum
    name: UniswapV3Pool
    network: mainnet
    source:
      address: "0x88e6A0c2dDD26FEEb64F039a2c41296FcB3f5640"
      abi: UniswapV3Pool
      startBlock: 12370624
    mapping:
      eventHandlers:
        - event: Swap(indexed address,indexed address,int256,int256,uint160,uint128,int24)
          handler: handleSwap

AssemblyScript handlers — not TypeScript. No nullable types, no closures, no many standard APIs. An error in the handler stops the subgraph indexing on that transaction. Important: add try-catch for operations that can fail (e.g., store.get() for an entity that may not exist).

How to Avoid Subgraph Indexing Stops?

Graph Node logs are monitored in real-time; on hasIndexingErrors = true an alert fires and an automatic node restart (via systemd or Kubernetes). Typical downtime on error — 150–300 seconds to recover. Additionally, for production we set up a watchdog that restarts Graph Node if subgraph lag exceeds 50 blocks.

Choosing Between Hosted Service and Decentralized Network

Graph Hosted Service (free, centralized) is deprecated in favor of Subgraph Studio + Graph Network. For production: deploy on Graph Network with GRT curation signal — the subgraph gets indexers proportional to curation.

Alternatives to The Graph: Ponder (TypeScript, self-hosted, easier to debug), Envio (ultra-fast indexer, supports EVM + non-EVM), Subsquid (TypeScript, own network), Moralis Streams (managed, webhook-based). Our experience shows: for high-load projects with unique logic, Ponder or Envio are more effective — they give full control over the process and do not require GRT tokenomics.

Webhooks and Real-Time Notifications

Alchemy Webhooks and QuickNode Streams allow receiving events in real-time via HTTP webhook or WebSocket. For monitoring addresses, new transactions, mints — this is faster than polling RPC.

Tenderly — platform for monitoring and alerts. You can set up an alert for a specific contract event, balance change, function call with certain parameters. Transaction simulation via Tenderly API is invaluable for debugging.

Monitoring and Observability

Minimum monitoring stack for a protocol:

On-chain: OpenZeppelin Defender Sentinel — watches contract events, triggers webhook or Autotask when conditions are met. Forta Network — community-maintained bots detect anomalies (large withdrawals, flash loans, governance attacks).

Infrastructure: Grafana + Prometheus for nodes, Datadog or Grafana Cloud for managed metrics. Alerts on: node is 10+ blocks behind, RPC latency >500ms, subgraph lag >100 blocks.

Uptime: Better Uptime or PagerDuty on RPC endpoint and subgraph health endpoint (The Graph provides _meta { hasIndexingErrors, block { number } }).

Why Is Monitoring Without Tenderly Insufficient?

Tenderly provides transaction simulation and detailed traces — critical for debugging subgraph and smart contract errors. Forta focuses on network anomalies, not your infrastructure. The combination of Tenderly plus a custom Grafana dashboard covers 90% of incident scenarios.

Multichain Infrastructure

A protocol on 5 chains = 5 separate RPC endpoints, 5 subgraphs, 5 monitoring configs. Manageable but requires deployment automation.

For subgraph multi-network deployment: graph deploy --network mainnet, graph deploy --network arbitrum-one etc. with a unified codebase and network-specific addresses in separate config files.

Chainlink CCIP and LayerZero for cross-chain messaging require monitoring of both chains and transactions on intermediate relayers. A reorg on the source chain after a confirmed mint on the target chain is a classic bridge problem. Solution: wait for finality (on Ethereum ~15 minutes after Merge for economic finality) before confirming on the target chain.

Infrastructure Setup Process

1. Audit current stack — determine chains, request volume, latency and availability requirements.
2. Architecture design — select providers, load balancing, redundancy.
3. Subgraph development — manifest → schema → handlers → testing on local Graph Node → deploy to testnet → mainnet.
4. Monitoring configuration — Tenderly alerts, Grafana dashboard, PagerDuty integration.
5. Documentation and runbook — what to do when: subgraph falls behind, RPC downtime, node desync.
6. Handover to operations — team training, access transfer, first month support.

What's Included

• Deployment of managed or self-hosted Ethereum, Polygon, BNB Chain nodes
• RPC layer setup with primary/fallback and load balancing
• Subgraph development and deployment for your protocol
• Monitoring connection (Tenderly, Grafana, alerts)
• Runbook and operations documentation
• Team training (up to 4 hours online)
• 30-day support after delivery

Timeline

All projects are managed in a GitHub/GitLab repository with CI/CD; configuration code stays with you. Order infrastructure deployment — we'll show how to cut costs by 20–30% without losing reliability. Get a consultation — we'll demonstrate how we deployed infrastructure for a protocol with large TVL on Ethereum and Arbitrum. Contact us.