No matter what checkout flow you have set up, customers are redirected to the Alipay website or mobile APP to complete payment, depending on if they are using a desktop or mobile device.
After clicking submit payment on your website, customers are redirected to the Alipay website.
They are given the option to scan a QR code with their mobile device (most common), or login using their Alipay account details (less common).
After clicking submit payment on your website, customers are presented with this screen, giving them the option to open the Alipay mobile APP to complete payment, or open the Alipay website to complete payment, as above.
If they select the mobile APP option, they will then complete the checkout process on the Alipay mobile APP, and then the mobile APP will redirect them to your payment confirmation page.