https://ttlc.intuit.com/community/rejections/help/what-if-i-entered-the-correct-agi-and-i-m-still-getting-an-e-file-reject/00/27031
for a 2021 joint return, you must use the AGI off each of your 2020 MFS returns.
if that doesn't work try 0. sometimes nothing works so you'll have to mail in your return.