Once you reach a subscriber limit, you will need to upgrade to paid plan to keep sending web push notification. You can check the pricing model here. For now, we only allow you to send 250 notifications to 2500 active subscribers in forever free plan. Other than this you can send an unlimited notification to 10,000 active subscribers in Pro, 50000 in Business and 150000 in Large Business Plan. You can have unlimited active subscribers once you go for Enterprise Plan.