User is trying to update the Net Bill amount when editing a draft invoice by changing the project's % Complete value and then clicking Recalculate Net Bill. However, it has no effect and the Net Bill remains the same.
This happens when the project does not have a contract amount. The Recalculate Net Bill option computes the Net Bill as:
% Complete x Contract Amount / 100
when Contract Amount > 0
If the contract amount is not defined or is $0, the Net Bill value is not recalculated and remains unchanged.