Total amount is Greater Than AP/Invoice.

hi experts,

i have one issue,

i want to make entry for Purchase Order Invoice(AP/Invoice) Greater Than Actual Amount.

Example,

I am ordering a item A,Total Quantity is 300 Kg.But Vendor Haveing that quantity 330 Kg.

& vendor Creating Invoice Agains 330 Kg. And I am Making Invoice 300 Kg.

So How can I make that extra 30 kg amount entry agains my Invoice(i.e 300 kg Invoice).

or remaining amount entry agains that(300 kg) Invoice.