I'm having the same issue. I filled out the page titled "We Need Some Information About Your 199A Income" by filling in my Ordinary Business Income that is on my Statement A as well as entering my UBIA of Qualified Property that it asks for. The rest of my Statement A is blank so I don't have anything else to enter. When I run the error check I get a message that Box 20 Code Z has been selected but not Section 199A information income has been entered on Statement A. It's maddening!
