Addendum:
See the info in my comment above first.
If you DID pay for PLUS by credit/debit card in the same account, but when you then go to download the 2017 return, you are still getting a message that you have to pay, then try this.
- Log out of TurboTax and any other Intuit accounts.
- Empty the browser Internet cache.
- Close the browser and reopen it.
- Then go to Online TurboTax and log in again, and try the download.
