All new accounts start with 10.000 credits, which is included in the initial package. These credits you're free to spend until they run out. Afterwards, you must buy more to continue sending.
Credits are calculated based on sent SMS messages.
At some point, you might not have enough credits to fulfil a certain campaign. Perhaps you have most of the credits but not enough for the entire sending. What happens then is that the campaign will be fulfilled, meaning that all SMS messages will be sent, but your credit balance will become negative.
When your balance is negative, or you're out of credits, you can still create SMS campaigns but not send them. Credit cost is calculated on schedule, so if you don't have enough credits at the time of sending, the SMS activity will be sent and your balance will become negative. This can happen if you schedule an SMS activity and there are more recipients at the time of sending than first calculated, or if you spend the SMS credits with another activity.
We will take the credits that you do have, and subtract the difference from the credits that you buy next time you refill. Your credit count will be displayed in negative until you buy more credits. For example: You had 500 credits, but your SMS activity cost 700. Your balance then became -200. When you buy 500 more credits, your balance will then be 300 credits.
After three hard bounces, bounced phone numbers are excluded from future sendings. Since credits are calculated per sent SMS messages, the three first bounces count as sent messages and are therefore charged. Previously bounced phone numbers do not incur a credit cost, since they're excluded from all future sendings, as long as they've bounced 3 times before. Only sent SMS messages count towards the final cost of your SMS activity.