$1,400 is the amount of the 3rd Stimulus payment. Did you already get the Stimulus payment they sent out last year starting March 2021? The IRS has records that show you were sent the 3rd stimulus payment so they removed the $1,400 Recovery Rebate Credit.
Do you have 1,400 on 1040 line 30? You might have tried to claim it again. Line 30 is only if you didn't get the full amount or qualify for more.
Did you get IRS letter 6475 saying what they sent you? If you didn't get the IRS letter 6475 saying what they sent you then check your bank statements and check your IRS account to see when and what they sent you.
Your Online Account | Internal Revenue Service
Request a trace for a missing third Stimulus payment
https://www.irs.gov/newsroom/questions-and-answers-about-the-third-economic-impact-payment-topic-j-p...Your Online Account | Internal Revenue Serv
