@jeffgiali
If nothing else works, have you tried efiling by using a 2020 AGI of 0 (zero)?
If someone filed the 2020 return real late in the year such as November 2021 or later, or if the IRS had not finished processing the return prior to November 2021, an AGI of 0 (zero) might be necessary for efiling.
Even if that's not the case, as a last resort sometimes it works unexpectedly. I would certainly try it before giving up.
