In order to send SMS your account needs to have SMS credits accredited to it. To top up your account press on the cart icon on the Platform toolbar and on the Buy SMS Credits option thereafter:
This will lead you to the online purchase screen:
Once on the Account Top Up screen you will be requested to fill your identification details on the left. If this is your first purchase you will be required to enter your payment details. From your second purchase onward, you will be able to use the payment details logged initially or change them as you see fit.
On the right you will be requested to choose the SMS bundle you wish to purchase. All bundles are non-limited in usage time.
After all details are entered you are to accept the Terms by checking the box and press on the Secured Purchase button.
Once the purchase is complete, a corresponding invoice will be sent to the email address you filled on the form. From here you will be able to proceed to the Sending Screen where your account balance will appear updated. As well, it will be updated on the Quota Screen accessible from the toolbar: