Pay for performance?

"Pay for performance. Subscriptions cost $xxx at the end of each month, but only if the system has made profitable trades."

Does this mean that a subscriber will be charged the subscription price if the system has made any profitable trades that month or only if the system nets out profitable for the month? E.g. if a system has 5 winning trades for a $500 gain and 10 losing trades for a $1000 loss (net -$500) then the above statement taken literally would still imply that subscribers have to pay (because the system did indeed make profitable trades). Is that the case?

The meaning is that payment is required if all trade net out to profitable.