If the letter is from the IRS it's fake because the IRS does not send letters or anything else for non-filing of state returns. if it's from the state it could be legit. you can go to the state's webpage and find a number to call to check. The other option is to check the filing status in Turbotax
Sign in to your TurboTax account and open Your tax returns & documents on the Tax Home screen. Your state return for 2021 should be listed as Filed, and your Return Status should say Accepted. If it says Started instead, your state return was never filed. if it's complete you can print it out, assuming all fees have been paid, and mail it in. following the basic Turbotax instructions for attachments and the instructions in the letter for filing.
if it's not complete, you'll need the desktop app to finish the state and file. If you have paid all your fees, try contacting support to see if they'll push a free desktop version. Otherwise, you'll need to purchase and download that year'sTurboTax software for PC or Mac, as TurboTax Online and the mobile app are only available for the current tax year.
