Recovery Rebate Credit 2021 incorrectly added for overage dependent

As I was entering my information for 2021, I was surprised when TurboTax indicated that I may have not received the full amount for the 3rd EIP payment.  I entered the correct amount ($2800) that we had received, but it indicated that we were eligible for an additional $1400.  After filing, we have now received a letter from the IRS indicating that we were not eligible for the $1400 due to our dependent being over the age qualification, and we now owe $1400 more to the IRS.  TurboTax had the birth date for this dependent, so why did the software indicate that we were eligible for this additional credit?  This was incorrect and should not have been included with our tax return.