In the dashboard, on the Plan&Billing page, you can see that the Premium and Business plans have Overage supported listed as a feature, while the Free, Pro and Startup plans do not. This article explain what that means.
When you exceed your plan's limits, several things happen. On the Free, Pro and Startup plans, requests will simply be rejected. You will be notified in advance when you reach 80% and 100% of your plan's limits. You can configure notifications in your dashboard on Account Settings.
Business, Premium and Custom plans support overages. That means that you won't notice any immediate changes when you go over your limits. We don't automatically charge for overages, but we will enforce limits if they're abused often. We will not deactivate your application or restrict connections without attempting to contact you first.
If you anticipate a spike in usage or a general increase in connections, then we recommend upgrading to a larger plan in advance or contacting our sales team.