Put the missed-receipt case in front of both authors together. Ask who owns the request while receipt is absent, what identifies the exchange, and what the operator sees after a timeout. Two descriptions of the happy path won't settle the disagreement.
Make the timeout example include a receipt arriving late. Otherwise they may agree to label it failed, then quietly attach its late reply to whatever request happens next. The original exchange needs to keep its identity.
And get that unresolved state into the operator explanation. People need to know who can reconcile it; they shouldn't have to solve the authors' disagreement by pressing the request button again.