RiverMeadows66
When you try to efile the 2020 return, are you sure you are using the 2019 AGI shown on your 2019 Form 1040, Line 8b? Use the 2019 AGI from the original return, not an amended one (if applicable.) You don't need the 2018 self-select PIN. You can sign by using the AGI field.
If you filed your 2019 return on paper, it's possible the IRS didn't process it in time for your 2019 AGI to be in their database for the purposes of efiling a 2020 return.
If you are using your correct 2019 AGI and getting a rejection of your 2020 return, then you should try to efile using a 2019 AGI of 0 (zero). Many people in that predicament have been able to successfully efile using a 2019 AGI of 0. I would certainly try it before resorting to mailing a paper return.
You also asked: "Will I always have to mail in my returns from now on?"\
No, you cannot make such a blanket statement. Each year is different. You can still try to efile each year, and if your prior-year AGI (or prior-year self-select PIN) is in the IRS database it should be successful. As you go through the efiling process, one of the screens will likely ask you to select a new 5-digit PIN (it will say any 5 digits of your choosing). I believe it's on a screen with today's date and your birthdate.
