The TT program computes the credit on line 30 using the information you entered into the program for the amount of advance stimulus payments you already received.
The IRS cross checks every Form 1040 with an amount on line 30 for the recovery rebate credit. If the IRS thinks you already got the EIP payment, you cannot get it again as a tax refund. If you claimed a recovery rebate credit for a payment already sent to you, they recalculated your refund.
Check your IRS account and see if the IRS sent your EIP payment. If they did, and you really did not receive it then they can trace it.
https://www.irs.gov/payments/view-your-tax-account
If you were issued a payment and have not received it, see How do I request a payment trace to track my first or second Economic Impact Payments?
