Additional payment on first federal voucher after amending my tax filing?

I already paid my first federal voucher. I later got a letter from the IRS requesting a form that I forgot to file (8962, not directly related to the voucher filing), but now I owe more in federal taxes after amending my return. The new vouchers on the amended return are for a higher amount now; how do I handle the difference I've already paid on the first voucher, and the higher amount stated on the new first voucher? Do I even need to pay this difference at all?