Debugging API Integration Issues

Learning Objective

By the end of this lesson, you will be able to describe a systematic approach for investigating an API integration problem, using payloads, status codes, logs, and job logs together.

Simple Explanation

Debugging an integration problem draws on nearly everything covered in this batch, plus debugging habits already familiar from earlier in this course. A reasonable order of investigation:

1. Check the status code first. This immediately narrows down whether the problem is with the request itself (4xx), the other system (5xx), or whether the call actually succeeded (2xx) and the problem lies elsewhere.
2. Check the logged request and response, covered in the Logging Integration Requests and Responses lesson, to see exactly what was sent and what came back.
3. Check the job log, exactly as covered in earlier debugging lessons in this course, for anything the RPGLE or CLLE program itself reported while making or handling the call.
4. Check the external system's own response or logs, if available, since a 5xx or unexpected response often points to a problem on the other side rather than in the IBM i program itself.

Why It Matters

An integration problem can originate in several different places: a malformed request, a genuine problem on the external system, a parsing mistake once a response comes back, or a bug in the IBM i program's own logic. Working through these checks in order, rather than guessing, narrows down the actual cause far more reliably, the same disciplined approach already used for debugging RPGLE and batch job problems earlier in this course.

Practical Example

Imagine an order fails to be created through an API integration. Checking the status code first shows a 400, immediately ruling out a problem on the external system's side. Checking the logged request shows the customer number field was accidentally left blank due to a parsing mistake covered in an earlier lesson in this batch. The job log confirms the RPGLE program reported no internal errors of its own, narrowing the actual problem down to how the request was built, rather than anywhere else in the chain.

This is a simplified, illustrative example rather than a specific real incident, but it reflects a genuinely common integration debugging scenario.

Common Confusions

"If the job log shows no errors, does that mean the integration problem must be somewhere else?" Not necessarily on its own, but it is a useful data point: a clean job log narrows the problem away from an unhandled RPGLE or CLLE error and toward the request itself, the external system's response, or how that response was parsed.

"Should I start by looking at the external system's logs first?" Usually not first. Checking the status code and the logged request and response on the IBM i side first is typically faster and often narrows the problem down before needing access to, or cooperation from, the external system.

"Is this a completely different debugging approach from the RPGLE and batch job debugging covered earlier in this course?" No. It follows the same underlying discipline, work from the most readily available evidence outward, applied to the additional integration-specific evidence: status codes, request/response logs, and the external system's own responses.

Quick Recap

• Start by checking the status code, then the logged request and response, then the job log, then the external system's own response or logs if needed.
• Working through evidence in this order narrows down whether a problem originates in the request, the IBM i program's logic, or the external system.
• This builds directly on the logging practices and error-handling vocabulary covered earlier in this batch, combined with the job log debugging habits already familiar from earlier in this course.

Try Asking the AI Tutor

Use the AI Tutor to ask follow-up questions about this lesson. For example, try asking:

• "Can you walk me through a short integration debugging scenario step by step, using this order of investigation?"
• "What would make you suspect the external system rather than the IBM i side when an integration call fails?"