When paying commissions on paid premiums, the presence of a payment does not necessarily guarantee a commission payout. Since fees aren't considered commissionable, the percentages of payments thought to be applied to fees can't be considered commissionable either.
Given a policy with a recurring billing schedule whose installments introduce a system fee, commission dollars can only apply to dollars out of payments against invoices that serve to pay off a portion of the premium, after fees. If a payment fails to do this, no commission can be awarded.
In this scenario, the total amount due on the term thus far has been paid in full, so the outstanding balance on the term should not be confused as a factor. However, because the payment applied in the second month does not exceed "commissionable amounts so far" minus billed fees, there is no new commissionable amount. Adding a single dollar more to the payment would result in a positive commissionable amount.