How do I report my receipt of interest payments from a seller-financed mortgage on undeveloped land (no residence)?

Enter the interest that you received from the buyer as if you had a 1099-INT form. 

In TurboTax, open your return and follow these steps:

1. Select Federal from the left side navigation.
2. Select Wages and Income from the top tab.
3. Scroll down to  Investments and Savings (1099-B, 1099-INT, 1099-DIV, Crypto) and Start/Review.
4. If you land on the Your investments and savings screen, scroll all the way down to Add investments.
5. Continue and on the Let's import your tax info screen, select Enter a different way. 
6. On the OK, let's start with one investment type screen, select 1099-INT and Continue.
7. On the How do you want to enter your 1099-INT? screen select Type it in myself.
8. On the Let's get the info from your 1099-INT screen, enter the borrower's name, SSN and if possible, address in the Received from box.
9. Continue with the onscreen interview until complete.