SMS Service Providers are required for sending SMS. We currently support Nexmo and Twilio. So create an account first and setup payment and other things such as API key, api secret etc first.
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Adding a New SMS Service Provider
After you setup your Nexmo or Twilio account, click on the New SMS Service Provider button
A dialog box will appear, choose Nexmo or Twilio.
Provide a name, API, token/api secret etc.
Click on the Save button
Edit
Click on the Edit button or the service provider name