Net Investment Income

Had a professional prepare taxes for 2023.  On my own this year, and want to be sure she got the Net Investment Income Tax right:

Sold a small retail business and carrying a contract for the new owner.  Income, less the interest is about $45K per year.  It includes only the goodwill and non-compete clause portion of the sale.  All the tangibles were paid for in cash at closing.

The full amount of the principal is showing up as capital gains on schedule D, and also as investment income on form 8960.  Just want to verify that this is correct. My small brain is having trouble understanding this as "investment" income.  THANKS!