There is no limit. You can send unlimited promotional messages with Mobile OTP Login and Order SMS Notifications Extension for Magento 2.

Read this guide on How to Configure Mobile OTP Login and Order SMS Notifications to Magento 2 to setup this extension to send promotional messages.

Here are the few more resource to help you get most out of this Magento 2 Mobile OTP Login and Order SMS Notifications Extension.

• How to Allow Login via Mobile Number OTP in Magento 2?
• How to Verify Customers Identity with Magento 2 Mobile OTP Login Extension
• What are SMS Order Notifications for eCommerce? What are it’s Benefits?
• How to Set New Order SMS Notification in Magento 2