Why do you have 2400 on 1040 line 30? Did you not get some of the Stimulus payments? How much did you get for the first and second round? Are you married? Do you have any dependents under 17?
You might have not entered the stimulus payments you already got or entered the wrong amount. Looks like you tried to claim the 2400 again that you already got. The first round was 2,400 for a couple.
