1200 sounds like the second Stimulus payment for married or Single with 1 dependent. Was 1200 on line 30?
A common adjustment is if you claimed the Recovery rebate credit on 1040 line 30 when you already got the Stimulus payment or got the second one after you filed or reported the wrong amounts or entered the wrong amounts in the 2 boxes. If you entered the total you got for both rounds in the same box it would think you didn't get the other one.
The IRS will be sending you a letter, so wait for it. They do not notify TT, but perhaps they adjusted your Recovery Rebate Credit because (1) you did not qualify for it; or (2) your 2020 income differed from 2019; or (3) their records indicate you were already sent it as a stimulus payment. (Some of those stimuli were sent as debit cards. Could you have received one, but threw it out as junk mail?)
Recovery Rebate Credit Frequently Asked Questions | Internal Revenue Service (irs.gov)