My return was rejected because my AGI and/or PIN was wrong. My AGI was correct and the system didn't ask me for last year's PIN. I'm concerned.
You would have received a rejection message that the Social Security number was on another tax return.
Your error is for the 2019 AGI only.
Try entering a 0 for the 2019 AGI and e-file again.
You should get a transcript and see what's been filed: https://www.irs.gov/individuals/get-transcript