Best practice

Idempotence

Idempotence is the property of Alipay sending back only one unique result for the same requests that were sent multiple times. Alipay checks the idempotence to keep an accurate transaction or refund result for each request. To help Alipay checks the idempotence, you need to take the following actions:

• For the same payment requests that were sent multiple times, provide the same out_trade_no for the same payment requests. Requests with the same out_trade_no are considered as the same transaction.
• For the same refund requests that were sent multiple times, provide the same out_trade_no and partner_transaction_id for refund requests that were sent multiple times. Requests with the same out_trade_no and partner_transaction_id are considered as the same transaction.

Alipay checks the idempotence for payment and refund requests in the following ways:

• For the payment requests with a same PID:

After receiving a payment request, Alipay checks the idempotence of out_trade_no (partner_transaction_id). Transactions with a same out_trade_no are considered as same transactions. Alipay then checks other information such as the buyer information and the transaction amount. If the information does not match with that in the Alipay system, errors will be returned. Otherwise, Alipay returns the real status of the transaction.

• For the refund request with a same PID:

After receiving a refund request, Alipay checks the idempotence of out_trade_no (partner_transaction_id) and partner_refund_id. Refunds with a same out_trade_no AND partner_transaction_id are considered as same transactions. Alipay then checks information such as the amount of the refund. If this information does not match with that in the Alipay system, errors will be returned. Otherwise, Alipay returns the real status of the refund.

For more details about idempotency, see API idempotency.