I'm trying to get into Zoho books and it mostly is suitable.  My issue/question is that I have 1 major customer I have that orders in blanket form and pays the invoice in total but I will hold the stock and deliver a few pieces at a time. 

With Zoho books I can only create a packing slip for the invoice amount rather than for a different amount.  

Am i missing something that allows me to do this or does the Zoho CRM do this or will the new Books inventory addon cover this?

Thanks

Keith