I have a similar problem because the IRS has not yet processed my 2019 paper return. They cashed my check, but did not record my return. I just today (2/12) re-sent my 2020 electronic return using "0" for my 2019 AGI. We'll see if that works. If not, I'll have to submit the darn thing by mail. Not looking forward to that. You can find out if your 2019 return was processed by going to irs.gov and accessing your account. You'll have to have your cell phone handy since they will eventually send you a message with a six-digit pin to use. Our tax dollars at work (yeah, right).
