onepage checkout – Adds the basket rule to the item already on sale

Prerequisites: If a payment gateway is selected for a specific set of items, the price must have a fixed discount.

Problem: Most items have an already reduced price. Defined under Catelog-> Manage products-> Special price

When a payment gateway is selected from the OnePageCheckOut page, I wish the item to be reduced relative to the main price.

Item Price – X
Special discount – Y
Purchase Basket Rule Fixed Discount for a Specific Gateway – Z

Currently, even if the discounted payment gateway is selected, the price of the item is always indicated by Y

Expected results – If the specific element is selected, X must be replaced by Z. Otherwise, the price must remain equal to Y.