The Recovery Rebate Credit is not for the advance child credit you received in 2021. It is for the 3rd stimulus payment you should have received in 2021. It is $1,400 per person entered on your tax return. You should have received Letter 6475 from the IRS showing the amount of 3rd stimulus payment received. If you are married, your spouse also should have received a Letter 6475. You were asked to enter the amount of the stimulus payment paid. If you indicated that you did Not receive the 3rd stimulus payment then that amount would have been entered on your Form 1040 Line 30 as the Recovery Rebate Credit.
Go to this IRS website for the Letter 6475 information - https://www.irs.gov/individuals/understanding-your-letter-6475
If your refund is short 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 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 are Married Filing Jointly also check your spouse's tax account.
If you checked your bank account in the March - May 2021 timeframe and there is not a 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-p...
