1) check your bank account for March-May, 2021. The fact that the IRS made the adjustment means they believe they sent you the $4200. There were TWO letters, one adressed to each spouse and they were to be ADDED together. So the answer to your first question is 'probably not'. Again, checking your bank account will confirm that you received the $4200 already.
2) the way the 3rd stimulus worked is that the IRS paid out the stimulus in March, 2021 as an ESTIMATE of what you were due. Then the 2021 TAX return was ACTUALLY what you were due. If the ESTIMATE was LARGER than the ACTUAL, you were NOT obligated to pay back the difference (in other words LIne 30 could not be less than zero). I suspect you received $4200 as that estimate and were eligible for $4200 on your 2021 tax return, so Line 30 should be zero (which is how the IRS effectively adjusted Line 30)
3) on your dependent, can you please explain whether they received the $1400 as a stimulus payment in march-may, 2021 or on Line 30 of their 1040 tax return. They way you wrote it, THEY received the $1400;which is different than YOU receiving the $1400 as your dependent. Can you please explain more specifically regarding the $1400 that went to your dependent? did THEY get it or did YOU get it? it matters
