Did you enter a 2020 AGI for both of you? If you filed as Married Filing Joint in 2020 then you need to enter the same 2020 AGI for both of you, even if only one had income.
If you filed as Married Filing Separate in 2020 & are now filing as Married Filing Joint, then you need to enter the 2020 AGI from each of your separate 2020 returns.
If all else fails, try using a Zero for the 2020 AGI
