This is such a "programmer problem".
So I'm ordering 10 items, but nooo, the software only allows "8 items per invoice". So the user has to create one invoice, then I pay that, then they make a second invoice and I have to deal with that and so on.
Alberto - you're fixing the wrong problem. Don't limit the number of items on the invoice, fix the reason they want to limit it in the first place.
cheers
Bruce