@ Alfie_E
I had the same problem and spent hours last night and this morning looking for the solution as to why the IRS rejected my return (3 times) due to "spouse's Prior Year AGI doesn't match their records". Apparently, it's a glitch in the app for joint filers, possibly in the IRS system itself, that recognizes the Prior Year AGI on your joint return as belonging to the taxpayer but not the spouse. Here is the solution that was suggested to me by a tech at FreeTaxUSA. Happy to say, it worked!
1. Go to the page that asks for your Prior Year AGI.
2. When asked if you filed a 2020 tax return, answer yes.
3. Even if you filed jointly in 2020, click on the option that "Only the taxpayer filed a return".
4. On the Prior Year AGI page, answer YES, that you have access to the primary taxpayers AGI.
5. When asked for Prior Year AGI, enter the correct 2020 Prior Year AGI, from your 2020 joint return, as if it's for the primary taxpayer only. This will make the app assume that the spouse's Prior Year AGI is 0.
6. Continue and ignore any alerts and fill out the rest of the pages until you can press the Send Tax Return button.
It worked for me, and my return was accepted this afternoon. Hope it works for you, too. Good luck!
