Thanks so much!
Really appreciate your help, especially when the error message is so vague and unhelpful. 🙂
This does not match what the IRS says here though:
https://www.irs.gov/filing/amended-return-freque[product key removed]ions
Can I file my amended return electronically?
Yes. If you need to amend your 2019, 2020 or 2021 Forms 1040 or 1040-SR you can now file Form 1040-X, Amended U.S. Individual Income Tax Return electronically using available tax software products.
