The default year-end date for an estate starting 4/13/2021 is 03/31/2022, unless a short year ending 12/31/2021 is chosen.

You said it was a calendar year estate, meaning the first year was 4/13/2021 through 12/31/2021. Was 2021, IF NEEDED, filed using that end date?

Was the SS4 requesting the estate's EIN filed using 12/31 as the annual end date?