Doing so gets the same message that the original poster mentioned i.e.,:
Looks like you didn't file with us last year or you filed using a TurboTax product that doesn't include access to prior-year returns.
So, the net result is you can't currently import any of your 2018 tax return info into your 2019 return -- even though (as the original poster did) I paid for the downloaded version of TT2019.
