Why Tax Classification code in Contract Management is not reflected in the AR invoice?

Summary:

Why Tax Classification code in Contract Management is not reflected in the AR invoice?

Content (please ensure you mask any confidential information):

We have created an AR invoice based on a contract in the Contract Management module. The contract document allowed us to input a tax classification code during the creation. But this tax classification code does not get transferred to the AR module invoice and our AR transaction includes the default tax rate code.

Why is that the AR transaction does not inherit the tax classification code from the contract in the contract management module please?

Thank you.