Premium SMS API is the most flexible service type in Fortumo. It allows you to create any payment service that you could think of, but it requires some programming skills and a web-server where you could host your program (for example as a PHP-script). Interaction between our server and your script will be conducted with HTTP GET requests.
Please note that API approval is generally complicated therefore we recommend our Web SDK product since the approval is faster and easier. You can find more information about our Web SDK product here.