1099 R Box 2b Taxable Amount Not Determined

Do you have a "Taxable amount not determined" checked in box 2b despite a taxable amount being reported in box 2a?

The IRS requires that your custodian report the full amount of your IRA distribution in box 1 (Gross distribution).

Box 2a (Taxable amount), also reports the full amount distributed unless you have directly rolled over your funds to another IRA.

If box 2b is checked, determine if you have made any non-deductible (after-tax) contributions to your IRA account, which may lower your taxable amount.