Diagnosing and Resolving Callback Issues

Callback (webhook) mechanisms are essential in a system for notifying integrated systems of transaction states. However, integration or infrastructure misconfigurations often disrupt callbacks. This guide outlines common callback issues and how to resolve them effectively.

Callback Not Received After Transaction Approval

The callback is not triggered or not received following an approved transaction.

Troubleshooting Steps

• 🔧Endpoint Configuration
  Ensure the callback URL is correctly set in the platform or CRM system. Include the complete path and required query parameters.
  ✅ Example: https://crm.example.com/api/v1/payout
• 🌐 URL Accessibility
  Verify that the callback endpoint is reachable and responds with 2xx HTTP status codes. Test using curl or Postman.
• 🔒 HTTPS Enforcement
  Callbacks may require secure connections. Ensure the URL begins with https://. Avoid automatic HTTP→HTTPS redirections that could block delivery.
• 📜 SSL Certificate Validity
  Check for SSL certificate mismatches or expirations. Tools like openssl can help validate the Common Name (CN) and Subject Alternative Names (SAN).
• 🔁 Retry Mechanisms
  Check whether failed callbacks are retried and confirm if your endpoint responds appropriately (e.g., 200 OK). Analyze server logs for dropped or rejected requests.

Callback on Transaction Failure

Need to confirm whether failed transactions (e.g., due to low blockchain fees) trigger error callbacks.

Technical Notes

• 📤 Callback Error Types
  Expect callbacks with statuses like FAILED, BLOCKED, or CANCELLED when a transaction doesn’t complete. Include error metadata for diagnostics.
• 🧩 Error Categorization
  Differentiate between retryable (e.g., temporary network errors) and terminal errors (e.g., invalid recipient address, compliance restrictions).
• 📡 Monitoring Systems
  Set up real-time monitoring using Prometheus, Grafana, or similar tools to track callback failures and abnormal status transitions.
• 🧪 Sandbox Testing
  Use sandbox environments to emulate transaction failures and validate callback behavior.
• 📈 Fee Estimation Logic
  Fees may vary (especially for blockchain networks). Always calculate maximum expected fees dynamically using real-time market data (ask/bid rates).

Callback Arrives with Empty Payload

Callback hits the endpoint, but the payload is missing or lacks the signature, triggering validation errors.

Troubleshooting Steps

• 📥 Payload Logging
  Enable full request logging (headers + body) to inspect actual payloads received by the server. Ensure your web server doesn’t truncate large payloads.
• 🔐 Security Middleware
  Firewalls or proxies may strip payloads. Validate all network layers (e.g., CDN, WAF, reverse proxy) are forwarding requests intact.
• 🧪 Manual Testing
  Use Postman or curl to manually POST sample payloads with and without signatures to test your endpoint logic.
• 🧰 Callback Handler Hardening
  Ensure the Callback handler properly checks for missing fields, empty JSON, or absent headers, and provides actionable error logs.
• 🧬 End-to-End Emulation
  Simulate full transaction flow in a controlled environment (e.g., using staging APIs and mock events) to confirm production-like callback behavior.

Summary

Efficient callback handling in financial systems requires:

• Precise configuration of callback endpoints
• Enforcement of HTTPS and SSL standards
• Error code parsing and status tracking
• Real-time monitoring and alerting
• Robust testing in staging and live environments

By proactively addressing these factors, financial systems can achieve reliable, secure, and observable callback flows.