I am using a downloaded version of TT Deluxe (so not online). I had the same issue and initially couldn't find a way around it. After a half hour on the phone with TT, we got it to work without reducing the amount of my refund:
1. Under Federal Taxes/Deductions and Credits/Charitable Donations -- delete any entries that you might have entered there (itemized).
2. Continue through that section until you are Done with Deductions.
3. Continue through the next few windows until you see "Charitable Cash Contributions under the CARES Act."
4. Do as instructed and enter the total amount of your cash contributions to charitable organizations up to $300.
After I did this, I was able to file without getting that error message.
