idempotency
The unique key assigned to the payment immediately from PaymentManager.startPaymentActivity. Used for disaster recovery if a crash occurs before the larger set of information reported to the payment callbacks.The idempotency key is assigned very early, and does not suggest anything about the payment's success or even validity. If valid, however, it can be used to refer to the payment in other calls to Square's Connect API. For example, an incomplete payment created using PaymentParameters.autocomplete=false can be completed with a call to /v2/payments/idempotencyKey/complete.