Our company has a history of issuing unconditional releases on progress payments with a zero amount if we have not received payment through the specified date on the release. None of our customers have even taken issue with this and they understand it means that no payment was received. Some even prefer this method. However, I am now dealing with a customer who is saying that a UP with a zero means that no payment is due and that we should have received a conditional. Have we been doing this wrong the whole time? Do I have any ground to stand on with her claim? How can I fight this?