Logging and monitoring are essential to ensure visibility, traceability, and operational awareness of payment flows.

They enable the Merchant to detect anomalies, troubleshoot issues, and ensure that transaction processing behaves correctly under real-world conditions, including failures, retries, and asynchronous events. The focus is not only on capturing system activity, but on enabling correct interpretation of that activity under production conditions.

Scope and Positioning

While other chapters define transaction flows, payload structures, and state semantics, this chapter focuses on how those interactions are observed, monitored, and diagnosed in real-world operation.

Logging and monitoring practices must ensure that:

• All relevant system and transaction events are observable and traceable
• Transaction flows can be reconstructed end-to-end
• Operational issues and anomalies can be detected promptly
• Systems can be diagnosed and recovered under failure conditions in a controlled manner

These practices support both real-time operational needs and post-incident analysis, and must be implemented as core operational capabilities across all environments.

Relationship with Transaction Processing

SPG payment processing involves multiple interaction points, including:

• API requests and responses
• Asynchronous notifications
• Internal processing and transaction state updates

Logging and monitoring must provide continuous visibility across all these stages, ensuring that no part of the transaction lifecycle is opaque.

This is particularly important in scenarios involving retries, delayed responses, or multiple updates affecting the same transaction, where consistency must be maintained and validated against the expected transaction lifecycle.

In such scenarios, logs and monitoring signals become a primary mechanism to understand system behavior, validate execution paths, and support reconciliation of transaction outcomes.

Observability of Asynchronous Flows

Asynchronous communication introduces additional complexity that must be observable and traceable.

• Events may be delayed, duplicated, or received out of order
• Processing may occur independently of the original request lifecycle

The Merchant system must ensure that:

• Asynchronous events are tracked from reception to processing
• Each event is correlated with its originating transaction
• Missing, duplicated, or inconsistent events can be detected

Observability of asynchronous flows is essential to maintain consistency when handling external inputs and transaction updates, particularly in environments where final outcomes are not immediately available.

Security and Data Protection Considerations

Logging and monitoring must be implemented without compromising security.

• Sensitive data must never be exposed through logs or monitoring systems
• Authentication credentials, tokens, and confidential identifiers must be protected
• Logging must balance diagnostic value with data protection requirements

Improper logging practices may introduce security vulnerabilities or lead to unintended data exposure, particularly when handling request and response payloads.

Operational Role

Logging and monitoring are critical for:

• Detecting abnormal system behavior
• Identifying failed or inconsistent transactions
• Supporting incident response and recovery
• Providing traceability for audit and compliance

They must be treated as core operational controls, integrated into system design and consistently enforced across all environments.

Failure to implement proper logging and monitoring may result in undetected issues, delayed incident response, and inability to diagnose or audit transaction behavior.

Key Principle

Observability must be enforced as a system-wide capability, ensuring that all transaction flows, state transitions, and external interactions can be monitored, traced, and interpreted under real-world conditions.