I think it is not possible, only the profit made over the prize can be used not the prize alone. Contact the service staff of your broker to get a better answer.

No, it's not allowed to pay your subscriptions using the prize you got from a broker. I asked my 3 brokers about your question, and they told me that it is impossible. The best way is to use your bonus wisely to get more profits and the profits will goes to the services you had subscribed.