In case anyone continues to have this issue:
When I went back to that 1099-NEC, I had NOT checked the box that said, "Boxes 5-7 have numbers in them," or whatever specifically it says. Reasonably, I thought that meant those boxes were blank on my TurboTax form, as they are on my paper documents. But when you DO check that box, a section drops down allowing you to enter values for Boxes 5-7, and that's where I could see that there was a "0" typed into Box 5. This was forcing a value for Box 6 in the TurboTax system.
I just deleted the "0" and then I could e-file.
