I don't know. I think you should have sent them the 2020 return with the estimates added on showing a refund. Actually I just got a similar letter for 2023. I tried to apply some of my 2023 refund to next year and they sent me a letter LTR0112C saying they didn't know what to do with it and wanted a tax return. I wrote them back. Don't know how long it will take them. In a couple months I guess I should make a IRS account and see if it gets credited to me.
