There can be a variety of reasons for a return to be rejected.
If you are preparing the return yourself, it is most likely caused by the tax year. The IRS does not allow electronic filing for prior year returns through self-preparation websites. They will require you to print, sign, and mail prior year returns.
If you do not believe that is the reason for the rejection, then you can find the rejection code in the email you received or by logging into your TurboTax account and selecting Fix my return. This article will have a list of rejection codes from the IRS and the explanation for each one.
I hope this resolves your issue with filing your 2021 amended return.
