With the promotion of mobile payment and long-term market education of WeChat/Alipay, their four-stage cashier interaction standard has become the de facto industry standard. After mastering 

 this standard process, it is actually very simple to become a cashier.

1) Pay and place an order

This is the first step in payment. After we select the product and place the order, we will enter the "checkout page" to show you the payment amount, product summary information, and allow you to choose the payment method. After you confirm, the order will be placed in the backend.

After placing an order, the server will return a cashier parameter. After obtaining this parameter, the payment platform can pull up the cashier and let the user jump to complete the payment. If the user chooses a local payment method such as "Quick, Balance Payment", the local cashier will be called. If the user chooses an external account such as WeChat or Alipay, the channel's cashier will be called.

The callback includes two parts, one is the return from the cashier, and the other is the payment result notification.

Return to the cashier : After the user completes the payment at the cashier, he or she needs to return to the platform where the transaction was initiated to complete subsequent operations.

Payment result notification : Although this method of jumping to the cashier is very safe, the user's payment result cannot be grasped by the "merchant or payment platform" that initiated the transaction. Therefore, the results need to be pushed to the initiator's platform through callbacks.

Merchant result query : There will be a short white screen page after returning to the initiator's page. This is the local results page to query the order results for the user. If the callback result has reached the payment system, you can query it locally. If not, you need to go to the channel to check the payment result, then record the account and complete the push of the result page.

User result notification : If the check is never returned, doesn’t it mean that neither the user nor the merchant knows? The designer also thought that the channel would not only notify the merchant's payment system, but also send text messages or APP messages to inform users that payment has been deducted.

The above is a common checkout payment process in the industry. When the network is normal, it is completed almost instantly, leaving you unaware of it. Even if there is a network abnormality, he can ensure that at least one person among the counterparties is clear about the payment result.

After understanding the four-stage processing method, let's go into the details of the technical implementation and see how the various modules within the system are connected and processed in series.

We see that before creating an order during the order process, we first follow up on the payment method selected by the user and read the configuration information of the cashier in the merchant system. The purpose of this is to verify which payment products the merchant has permission to use, and the cashier should give it to him How to show.

The payment order process includes two processes:

Create a payment order : First, create a payment order locally. If a channel cashier is involved, it must also be created simultaneously.

Obtain cashier parameters : The second step is to generate cashier parameters and prepare for calling the cashier. The checkout parameter is generally a link or access token (this will be described in detail later).

Cashier jump : After obtaining the cashier parameters, the next step is to let the user jump to the designated cashier for payment. This step mainly involves converting the parameters between the "cashier system" and "channel cashier" and jumping to the cashier.

Secondary development : This is also a key location for whether secondary packaging is required at the channel checkout. For example, when we aggregate QR codes, here we can decide whether to jump to the "WeChat official account" or "WeChat official account" based on the APP the user scans. "Alipay service window" allows users to complete the jump selection without any sense.

Payment result registration : In order to know in time whether the user has completed the payment at the channel cashier, the cashier provider must give the transaction initiator a payment result notification, so that the initiator can register the account.

Timely response result : As the initiator, you must also complete the account registration and give the payment channel a "successful" response result, telling the channel that I have completed the account. What will happen if you don't return? In order to ensure that you can accept it successfully, the channel will continue to send you result notifications at certain intervals until you reply or the specified number or time is exceeded.

Page return : After completing the payment, you need to return to the merchant results page. This result page is usually set in the merchant backend of the channel or the return address is obtained through the integrated SDK.

Result query : After the page is returned, the local results page still does not know whether the order was successfully recorded, whether there is a discount, whether the user fee is deducted, etc., so a result query is required. If it is not checked back, the user will be asked to actively confirm the order results, and the system will scan the results regularly until the final results of the payment system and channel are consistent.

User notification : This handles the interaction between the payment channel and the user, including in-APP notifications, SMS notifications and other forms. The intermediary merchant system and the payment system themselves do not need to be processed. Its purpose is to ensure that users understand the payment results and prevent orders from being tampered with.