DirectPay: Wrong Tax Year

Looking for a "second opinion" from any tax experts on this:  A family member discovered that the IRS won't make an auto-pay debit for less than the agreed-upon monthly amount on a payment plan, so needed to use DirectPay for the final pay-off. Trouble is, the payment was wrongly marked for tax year 2020 instead of 2019 (plan was started in 2020). Will they automatically apply this to any remaining balance, or must the payment be re-initiated and then they'll eventually refund the excess? Thanks!