tax is calculating based on assessable value instead of transaction line amount

Summary:

A manual sales order has two items, one is taxable and nontaxable. The client not maintaining the price list but instead that they are adjusting the price manually and updating the assessable value manually

at the AR transaction level, there are Four lines, the order line with Zero price and the adjustment line with Price, My issue is tax is calculated Based on the assessable value instead of the transaction amount, because of this tax is doubled.

Example:

How to enable the tax calculation based on the amount instead of Assessable value.

thanks in advance.