How can I add a serial in zBooks if I do not have the BILL but I have the item and packing slip with serial

How can I add a serial in zBooks if I do not have the BILL but I have the item and packing slip with serial

So my warehouse receive in Stock (in zInventory) by selecting "Receive All" on the PO.
BUT...
My accounts team have not received a BILL so we can't ADD a serial number because SERIALS can only be added on BILLs.
However...
My accounts team using zBooks can't convert the PO into a BILL because the PO was created in zInventory (so says zSupport email to me)

So...
We want to invoice an item which shows stock of one
BUT...
I can't invoice because I don't have a serial number against the item so my Accounts team try to create a BILL but... start the loop all over again!


Does anybody else not find this weird? Is a simple process meant to be so confusing and difficult?
....

I use Zoho CRM, it's great, 
I use Reports, it's great, 
I use Creator, it's great, 
I use Sales IQ, it's great
I use Marketing, it's great
I use Sprints, it's very good
I use Cliq, it's very good

BUT zBooks and zInventory are just abysmal when it relates to a real world distribution business. I've been testing for a couple of months trying to find work arounds unsuccessfuly. So frustrating... rant over!!