I had to amend my 2021 and 2022 returns to report excess Roth IRA contributions. I was able to do it with TurboTax online and then tried to e-file amended returns. 2022 e-filing went smoothly but for 2021 I encountered an error. TurboTax allowed me to e-file but the transmission failed.
What could be the reason for the failure? I've read that e-filing option for 2021 amendments was not possible but TT does provide e-filing option.