You are correct; the IRS uses the AGI for the prior year return to identify taxpayers in order to combat fraudulent returns.  The AGI for both taxpayers on a joint return will be the same; no matter who earned the income. 

However, if the return is rejected due to the spouse AGI not matching, then enter a zero for your spouse's prior year AGI since this is first-time filing for that social security number. 

[edited 3/1/2021 9:57am EST]

Thank you very much for your reply. 

Let me clarify this just to make sure. 

So suppose our AGI for the joint return last year was $50,000. 

And it is okay to say my spouse's AGI was $50,000? 

That is correct.

Here are where you can locate AGI amount on different lines:

• Line 11 on Form 1040 and 1040-SR (for tax year 2020)
• Line 8b on Form 1040 and 1040-SR (for tax year 2019)
• Line 7 on Form 1040 (for tax year 2018)
• Line 21 on Form 1040A (for tax years before 2018)
• Line 4 on Form 1040EZ (for tax years before 2018)
• Line 35 on Form 1040NR

For more information, click here: AGI

@ paulmuzic

I followed your suggestion and it was rejected. 

I put $0 for my spouse's 2019 AGI this time. 

Hope this works.