We notify you before this happens. You can change your Credit Threshold in User Settings-Notifications so we can alert you to take action. We don't automatically auto-bill for overage. The user sending the message will receive 1 email per day when you are low in credits.
If you run out of credits but have an ongoing campaign, you will still be able to receive calls and text. You just wouldn't be able send messages or make calls. This puts the control in your hand.
Then, you can buy some more—we’ve got a choice of ‘credit buckets’ to choose from. They match the per month plan amount and price. Alternatively, upgrade your plan.
The price for each bucket of messaging credits matches the price for one month of any of our plans.