My return keeps getting rejected because of my AGI it’s saying it’s not 0 for 2021 even tho this is my first time filing so I wouldn’t have a 2021 AGI so what do I do?

Sounds like a gap in that process, so probably you just have to print it out and mail it in this one time.

If filing with zero is rejected then file again but select the option that you did not file last year.  The IRS does not see that question and it will allow you to e-file with no AGI question.