Post Edit formula - FSA - Do not want negative for communicated values

Summary:

Looking for a Post Edit election Fast formula that evaluates the communicated amount and returns an error when that amount on the FSA change is negative. We do not want to prevent reductions to annual amounts, but we do not want someone to reduce the election where it creates a negative.

Can we use CMCD_RT_VAL in some way to check this in a post edit election formula? Not a payroll client so unable to use a payroll balance, but using the estimated amounts should meet the need.

Content (required): Other suggestions would work as well as it does not have to be a post edit election formula, but these seems like the obvious choice.