My efiling was rejected because of my 2020 AGI. I have my 2020 1040 and tax return transcript off the IRS website. The AGI is the same, so why is it being rejected?

ENTER 0 FOR AGI. The IRS took a long time last year to process 2020 returns so the AGI didn't get entered in time.  Especially if you mailed it.  That works for most people. See,
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

How to correct the AGI in the Online version
https://ttlc.intuit.com/community/agi/help/where-do-i-correct-my-agi-in-turbotax-online/00/26311

If you can’t get it to efile you will have to print and mail it.
https://ttlc.intuit.com/community/printing/help/how-do-i-print-and-mail-my-return-in-turbotax-online/00/26258

Be sure to attach copies of your W2s and any 1099s that have withholding on them.  You have to mail federal and state in separate envelopes because they go to different places.  Get a tracking number from the post office when you mail them for proof of filing.

Thanks for the quick response. I did see “0” was an option. Will that work even if my return was processed and I received my return?

Thanks again! 

Probably will work.   Try it.  Nothing to lose.

Will do.