So you DID receive principal in 2017 and reported that OK?
It sounds like you didn't transfer over 2017 into 2018. "In fact I had to download the TT software" - for 2017 I presume. Yet now you're back to using online? If your competed your 2017 income tax return on your computer then that's where the .tax2017 file is so that's the file you need to transfer into the 2018 program.
Even so, if you didn't transfer the 2017 income tax return into 2018 that doesn't prevent you from doing the installment sale online. You just re-enter the 2017 information again and then TurboTax asks about 2018.
Tom Young
