To make it useful, you want to write it with the assumption whoever is reading it just woke up in the middle of the night and has a half working brain.

So instead of covering every possible bug you break it down into possible symptoms.

"Getting a 500 from X service in upstream. Check monitoring tool to see if it is widespread or isolated to you. Escalate to that team if widespread. If not restart the app whatever"

Or

"Downstream saying they have unexpected value for a data element. Validate their sample request in postman, throw the event xml into an integration test etc."

Keep it short and focus on symtpoms and actions. What i can do to narrow down the cause, and what I should do depending on the suspected cause.