Screw acquiring to a self-written site

Screw an additional form of payment to the site kingkongpizza.ru through the API https://moduldev.atlassian.net/wiki/spaces/IE/pages/28934183/10 QR -

The total amount in the shopping cart should be recalculated with a 1% discount.
In the admin panel of the site should be displayed payment / underpayment of the formed order.