I've done charity work and can't send a $0 invoice to them, it is an odd amount because you can only discount 99.99%. Have also done some pre-marketing services for a client prior to them signing on formally and want to send a $0 invoice to show value delivered! PLEASE FIX THIS! I have invoices sitting out there for $0.06 and $0.09 cents because you can't discount 100% or send $0.