Yeah...you unfortunately are on the wrong payment page...that page is used if NC sends you a letter next month or next year because they think you didn't pay enough this year..
Here's the proper page...when you start in on the D-400V payment, it starts out the same, but doesn't ask for the notice number.
hhttps://www.ncdor.gov/taxes-forms/individual-income-tax
And click on the "Pay Original Tax Due" in the right sidebar as you scroll down to the main part of the page.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*