Did excess Roth IRA conversion due to income limits. Have amount for box 1 and the earnings for box 2 of 1099-R. Age 65, not early distribution. Need codes for box 7.

Creating 1099-R. I can find a list of possible codes, but no explanation of each. Best I can come up with is 8 J, but only guessing. I am only trying to get the earnings recognized in TT so correct taxes paid. In same year so no penalty.