You can cancel the auto renewal of your SMS subscription. After cancelling, when you use up all your SMS credit, your customers will not receive SMS notifications.
Step-by-step guide:
Go to your Admin page.
Click on “Account settings” in the bottom left corner.
Click on Subscription
Next to your SMS package, click on Turn off auto renew.
Click on "Turn off" button.
If you turn off auto-renewal, SMS reminders will stop when you run out of credits.
Clients will not receive SMS reminders and might miss appointments.