When sending SMS messages, using either the Sinch SMS API or the Conversation API with an SMS channel, you must have at least one service plan associated with your account.
Note: Usually, each Sinch account is provided one service plan upon creation.
In addition to using existing service plans, you can also create a new service plan for use with SMS.
To create a new service plan:
After creating a new service plan, you must assign at least one virtual number to the service plan. You can also set the callback URL for the service plan.