That sounds like the difference. 750+652= 1402.00 You must have 1400 on line 30. Line 30 is only if you didn't get the full amount or qualify for more. Double check your bank statements and see if you got it a year ago.
If the IRS thinks they sent it to you but you didn't get it request a trace for a missing third Stimulus payment
https://www.irs.gov/newsroom/questions-and-answers-about-the-third-economic-impact-payment-topic-j-p...
