....has to be something else...like a high income that requires either the form 8959 to calculate extra Medicare tax, not SS tax. ....or, that might be the result of an entry error in box 6,........ or a missing box 12 code B or N entry, or certain box 14 entries for Medicare taxes if you are a RR employee.....(or you have self-employment income...but a BIG upgrade is required for that)
_________________________________
The W-2C notice is probably just a coincidental fluke. Increase your box 4 to the next even $1 and the W-2C notice will likely go away, and the 8959 form would still be needed.
_____________________
I'd point you to Customer Support on the phone...but FREE users don't get phone support (they don't have to if you aren't paying them anything).....and I'm just another user......and all you can hope for is someone stumbles on this post who has had that "exact" issue before knows how to fix it.....if it is indeed fixable...your tax return may need the form 8959 anyhow due to your income situation.
https://www.irs.gov/pub/irs-prior/f8959--2020.pdf
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
