Preventing duplicates

Send-time duplication is the failure mode you most want to prevent: two notifications to the same signer because a network blip caused your client to retry without an idempotency key.

Always pass Idempotency-Key on:

• POST /v1/envelopes/{id}/send
• POST /v1/envelopes (when sending immediately via "send": true)
• POST /v1/signers/{id}/sign-url
• POST /v1/webhooks (creating a webhook is otherwise duplicative)

For pure read operations (GET …), idempotency keys are accepted but unused.