@cep1021 - that IRS letter lists multiple reasons for the adjustment, but doesn't specifically state which one it is. So while your AGI MAY be the reason for the adjustment, it is highly unlikely.
what was your AGI (line 11 of Form 1040) ? unless it was above, $75,000, your income did not matter.
more likely, the issue is related to how much you received last year (check your bank statements between March and May, 2021) compared to what you entered into TT that you had already received.
If those two numbers did not match (and the IRS knows what they direct deposited into your bank account), the IRS adjusted the difference.
