Beware that Sandbox mode is only available for the REST API.
A sandbox system is available to you for testing. The sandbox will not modify your account in any way, but will respond normally to your requests. In other words if you use the sandbox to get the number of credits on your account, it will provide the correct number.
However if you use it to transfer credits between accounts, it will simulate a successful transfer (assuming you have enough credits on the account, and provide valid target account details, etc.) but it will not actually modify the number of credits on either account.
Similarly, the sandbox system will not actually send SMS messages and will not deduct credits for simulated sends.
The sandbox system is available at the URL:
i.e. to use the sandbox simply replace this part of the resource URL:
For example, the credits resource URL becomes:
The sandbox is restricted to a certain number of requests per minute. So you should not use it to test bulk SMS sends. This to reduce load on our servers, in order to guarantee a good service to all our users. There is no restriction on SMS sends onthe live system.