Create a subscription

A unique string of 1 to 255 characters for this operation. A key belongs to the business across every endpoint for 24 hours, so give each operation its own key, for example invoice-order-1042 and refund-order-1042, not the order id alone. A retry with the same key on the same endpoint and with the same body returns the stored response with the header Idempotent-Replayed: true. The same key with a different body or on another endpoint returns 409 idempotency_conflict. Errors are not stored, so a request that failed can be retried with the same key, even with a corrected body. While the first request with a key is still running, a retry gets 409 idempotency_conflict with Retry-After: 1.