The third Economic Impact Payment of $1400 per person was sent out in March of 2021. The IRS may be saying you got it and are asking for it again on you return.
Does the IRS website indicate that you were sent less than what was reported on your federal tax return Form 1040 Line 34? - https://www.irs.gov/refunds
If your refund is short $1,400 then that is because you said you did not receive the 3rd stimulus payment and the IRS has records that show you were sent the 3rd stimulus payment so they removed the $1,400 Recovery Rebate Credit that was entered on Form 1040 Line 30.
Go to this IRS website for your tax account to see if the 3rd stimulus payment is entered - https://www.irs.gov/payments/your-online-account
If you checked your bank account in the March - May 2021 timeframe and there is not a $1,400 EIP3 payment from the IRS then go to this IRS website for how to start a trace on the payment - https://www.irs.gov/newsroom/questions-and-answers-about-the-third-economic-impact-payment-topic-j-payment-issued-but-lost-stolen-destroyed-or-not-received