Webhooks redeliver
Commerce and carrier platforms repeat events until your endpoint acknowledges them.
Safe print retries
Retry the request without printing the job twice.
Physical side effects need a stable identity. Send the same idempotency key with the same request and RocketPrint returns the original job instead of creating another one.
Same key + same input = same job
The API marks the response as an idempotent replay; changed input with the same key is rejected.
The operational gap
A network timeout does not tell you whether paper happened.
If your worker loses the response after RocketPrint accepted the request, blindly trying again can create a duplicate physical artifact.
Workers retry
Queue systems rerun jobs after crashes and ambiguous timeouts.
Paper cannot be rolled back
A second label or receipt is not just duplicate data; it can become a real operational error.
The RocketPrint path
Derive identity from the business event.
A good key is deterministic, specific to the artifact, and stable for every retry of the same intent.
Choose the source ID
Start with the order, shipment, return, work order, or receipt ID your system already owns.
Add the artifact
Include label, slip, receipt, or destination when one record can legitimately print more than once.
Reuse on every retry
Keep the request body and key identical until you receive or recover the original job.
What changes
Retries become routine instead of dangerous.
Webhook safe
Repeated delivery of the same event can return the first job.
Timeout safe
A missing HTTP response no longer forces you to guess whether creation succeeded.
Mismatch detection
Reusing a key with different input returns a conflict instead of silently doing the wrong thing.
Plain HTTP semantics
New jobs return 201; idempotent replays return 200 with a response header.
Start with one printer
Make the physical step part of the workflow.
Install RocketPrint Station beside a printer, send one request, and keep the job ID. That is the whole path.