What should I enter into Turbo Tax for Box 2a? My CSA-1099-R shows "UNKNOWN" in box 2a.

No, don't enter $0 in box 2a.   Form CSA1099-R is a variation of Form 1099-R and it's an annuity issued to federal retirees. When you have a CSA 1099-R, you may have to determine the taxable portion of your distribution and you have to let TurboTax know that you are entering a CSA 1099-R. TurboTax will guide you through to determine the taxable amount.

If you entered your CSA 1099-R in the wrong spot, you'll have to delete it and follow the instructions below to enter it in the correct area. For TurboTax Online:

1. Open TurboTax and go to 1099-R.
2. Go to Income & Expenses
3. Select Review/Edit
4. Go to Form 1009-R
5. Select Add/Edit
6. Select the trash can next to the 1099-R that you want to delete

Next, review the TurboTax article Where do I enter my CSA 1099-R? for detailed instructions to enter your Form CSA-1099-R.