Contract Amendment effective Date Use

Summary:

Whats the exact functionality of Contracts Amendment Effective date?

Content (required): In our case we Have a external contract :- Initial Contribution % is 100% . We amendate the contract, changed the Contribution % as 50 % and Put the Amendment effective date as 8th July 2023.

Created a cost for 1st July 2023 and Generated the Invoice with Bill through and Invoice date as 5th July 2023.

Invoice Generated was with 50% of the value i.e. the new date.

Shouldn't it be with 100% Value as the Expenditure Item date and Invoice date was previous to that of Amendment effective date ?

Would be great if someone can help understand this , also provide some doc for the same