To add credits to your account select Manage Account -> Purchase SMS credits. Take note of the unit price as this is your cost per SMS message. The next step is to add the quantity that you wish to purchase and select calculate.

You will be given an order total, once you are ready you can proceed with payment of the credits by credit card or raise an invoice to your account. Please note that you must have enough credits for a SMS send or your SMS will not be sent.