Alipay callback uses HTTP request, and the payment result is sent to the callback URL provided by the merchant in the form of POST request. According to the 51CTO blog query, after receiving the callback request, the merchant server needs to verify and process the received parameters. After the user completes the payment, Alipay will notify the merchant of the payment result through server callback so that the merchant can update the order status or perform other business processing in a timely manner.