This was an issue that was brought up at my area stakeholder liaison monthly meeting.  The system doesn't allow ES payments for 2024 anymore (even though some folks in disaster areas still have time to make them timely).  The only viable options are extension payment and balance due payment.  Extension payments have a line on the tax return (Sch 3 Line 10).  Balance due payments do not.  Some folks suggested putting the payment on Sch 3 Line 13z.

I think entering the payments as an estimate is as good as anything else but there might be a matching notice later.  I had a client in this situation and told him to just mail the payment with the ES voucher.  We'll see if that works. <shrug>

Rick