@sas52 here is what i think occured:
When you filled out the Turbo Tax inteview process, I suspect you responded that you didn't receive anything. And if your joint income (no dependents) was about $158,800 (look at Line 11 of Form 1040), the Recovery Rebate would have been calculated as $336. THerefore that is what ended up on Line 30.
But the IRS records are that they sent you $876.40. Those 2 letters: they should be Letter 6475 and state that you received $876.40 ALREADY.
Therefore since you received more than you were eligible for, the IRS adjusted Line 30 to zero. Note: by law, you are not required to return stimulus if you received more last spring than what you are now eligible for.
Suggestions:
1) go back to your bank statements from last March - May, 2021 and see if there was a deposit for 876.40 from the IRS. if yes, then all is good. You received what you were entitled to and the IRS adjusted your return.
2) If you have no record of receiving the $876.40, despite the fact the IRS records indicate they sent it to you, you'll have to complete and send in a 'trace' form to the US Treasury to reconcile the issue.
https://www.irs.gov/pub/irs-pdf/f3911.pdf
