Have you tried to enter the code and then the amount?
Box 12 codes are:
A -- Uncollected Social Security or RRTA tax on tips
B -- Uncollected Medicare tax on tips
M -- Uncollected Social Security or RRTA tax on taxable cost of group-term life insurance over $50,000 (former employees only)
N -- Uncollected Medicare tax on taxable cost of group-term life insurance over $50,000 (former employees only)
