Hi,
In this basically it is one invoice with two payment terms.
So leave the NS Due date of the orignal invoice.
Then you send the invoice requesting a partial payment of US$ $4,847 ( we can send them a letter to tell this is for pre-payment if needed)
We should not mix invoice with payment terms& conditions.
So we give them the invoice total& a receipt for the US $4,847 but we do not split the invoice into 2.