Administrator needs to enable debug logging for a Content Delivery microservice.

As noted in documentation, modify the logback.xml file in config directory of the microservice.
https://docs.sdl.com/LiveContent/content/en-US/SDL%20Tridion%20Sites-v2/GUID-7178C850-FB79-49F7-99FC-316D105FA704

In order to avoid an overly large log, it is advisable to:
1. Stop microservice.
2. Rename or remove existing log.
3. Change the log.level param to have value DEBUG rather than ERROR.

<property name="log.level" value="ERROR"/>

4. Start microservice, reproduce issue, and verify there are relevant log events in the log.
5. After the issue for which debug logs are required has been captured in log, it is advisable to revert log.level param to avoid slowing down the microservice and filling up the hard disk.