The cost of campaigns can sometimes surpass that of the budget. This is due to the nature of push notifications, along with our cost structure CPC (cost per click).
When a push notification appears on a user's screen, there is a normal delay between when the push notification is sent out and when the user clicks on it. This delay makes it more difficult to implement strict budgetary lines when you are dealing with such high volumes, normal in this industry. To combat this delay, our servers calculate your campaigns average CTR (click-through rate) and they send out only enough push notifications to finish your budget, based on its average CTR. If there is an inconsistent spike in the CTR at the end of your budget, it can lead to overspending beyond your budget.
For example, let's say you have $5 left of your budget for an active campaign with a CPC of ¢05 and an average CTR of 1%. Theoretically, you would need 10,000 more impressions to reach your budget. Now let's say that in those last 10,000 impressions, you receive 400 clicks instead of the expected 100. You would be charged $20 ($15 over your budget). We do our best to minimize this as much as possible, but despite our efforts, it isn't abnormal for these kinds of things to happen.
If this happens to you and it results in your balance becoming negative, don't worry and simply talk to your account manager.