> For the complete documentation index, see [llms.txt](https://stephen-tsoi.gitbook.io/stephen-tsoi-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://stephen-tsoi.gitbook.io/stephen-tsoi-docs/messaging-troubleshooting/a-missing-event-among-billions-how-we-found-it-on-an-event-mesh/day-11-13-use-case-6-filtered-by-apm.md).
# Day 11/13 Use Case 6: Filtered by APM
**The event is filtered by a 3rd party APM library.**
In order to enable end-to-end tracing, traditional Application Performance (APM) tools typically install an APM agent on the target server. This agent intercepts the communication between the application and client messaging library, inserting some additional fields (trace information) into the event message header on the publisher side. On the consumer side, the APM library extracts the trace information from these fields before processing the event from the client messaging library.
One issue we have encountered in the past is when the publisher’s APM agent inserts an invalid value into the event message header. As a result, the consumer’s APM library filters out this event from the event broker and automatically discards it, causing the event to be missed in the entire process.
To troubleshoot this type of issue, you can use a well-tested program to subscribe to a specific topic. This ensures that the event is successfully received by the event broker. By comparing the event between the temporary queue and the consumer, you can identify the point at which the event is missed.
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