They want a promotion for their members. To push to purchase more. There is no promotion. Therefore, these members are likely to buy, it's a no for now.
They want promotions for their members. To push for a greater order. It does this promotion. Thus, the opportunity to purchase these members are not yet in now.
They want the promotion for their members. To bring more order, it is this promotion. Therefore the opportunity to these members to buy is not in right now.