Your KPI Result can be calculating correctly, but displaying as negative rather than positive value.

If one Account Group is using accounts of different types it will follow the formula of: (Income - CoGs - Expenses) = Net Income Value

Therefore, if the CoGs and/or Expenses are higher than the Income, the result will be a negative income amount.

To report this as a positive, construct the KPI using the individual account types:

(CoGs + Expenses) - (Income) = Net Expense Value