Line 30 is only if you didn't get the full amount or qualify for more. The IRS records show they sent you the 1400 last year. But you tried to claim it again.
Double check your bank accounts and check your IRS account (both accounts if married) to see how much the IRS sent you.
https://www.irs.gov/payments/your-online-account
If you didn't get the 3rd Stimulus check but the IRS shows they sent it to you then request a trace for a missing third Stimulus payment
https://www.irs.gov/newsroom/questions-and-answers-about-the-third-round-economic-impact-payment-top...
