Below is the irs detailed letter of possible causes but does not say which one is the cause.
We changed the amount claimed as Recovery Rebate Credit on your tax return. The error was in one or more of the following:
The Social Security number of one or more individuals claimed as a qualifying dependent was missing or incomplete.
The last name of one or more individuals claimed as a qualifying dependent does not match our records.
One or more individuals claimed as a qualifying dependent exceeds the age limit.
Your adjusted gross income exceeds $75,000 ($150,000 if married filing jointly, $112,500 if head of household).
The amount was computed incorrectly.
