You chose the wrong payment entry point on the NC website: The starting entry page looks exactly the same, but the URL is a bit different...go here:
https://www.ncdor.gov/taxes-forms/individual-income-tax
Then click on the "Pay Original Tax Due" button on the rt-side:
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____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*