Pre Pay PO % of Total Value

Hi,

Not sure how to do this. We have Purchase Order For £1000. The supplier wants 40% upfront. The 40% doesn't match off against the purchase Order Lines. E.g. Line 1 is for £100 , line 2 is for £900.

What I would like to do is match the £400 against the PO and then process the £400 payment. Then when the final invoice comes is to net off the £400 and pay the £600.

Could anybody help on this one.

Thanks in advance.