No response. Was the booking created?

A timeout means uncertainty

The request may have succeeded even if the response was lost. Starting a new operation with a new identifier can create a second booking. Automatically reversing payment could leave a successful booking unpaid.

Retry, look up, resolve

Safe retries preserve the same logical operation, identifier and payload within the API contract and a bounded retry policy. When that policy is exhausted, use lookup. Confirmed success completes the operation without another booking. Confirmed absence of a booking permits reversal under this scenario’s agreed procedure. An unknown outcome stays unknown: retain it for reconciliation and tell the user clearly. A missing lookup entry does not prove non-execution unless the API contract guarantees that meaning.

Boundaries of the patterns

Idempotency prevents repeated execution from creating an additional effect within an agreed scope. Lookup establishes the outcome. Reversal is a compensating operation with its own conditions and possible failures; it does not magically roll back all history. Confirm the semantics and timing of the actual API.

The sequence and reversal condition are assumptions of this scenario, not universal rules for every payment system.