4.1.1 Payment flow

User wants to buy goods and make an order to pay
The merchant receives the payment request from the user , then calls the pay api to complete the payment
Obtain the payment result using one of the following methods:

Synchronous: return the result directly in the response to the pay request.
Asynchronous notification: set the address for receiving asynchronous notifications. When the payment is success or fail, UQPAY uses notify to send asynchronous notifications to you.
Inquiry: Call the detail API to check the payment request status.