I am creating a webhook subscription for Instant Messages (SMS) using the subscription endpoint on the ringcentral API. Instant Message Webhook Doc
/restapi/v1.0/account/{accountId}/extension/{extensionId}/message-store/instant?type=SMS
A subscription can be created for receiving messages from numbers from a specific extension. Is it possible to create subscriptions for specific phone numbers rather than all the numbers in the extension?
Unfortunately, there is no parameter to set for notification for a particular number under an extension. You will need to parse the notification message and filter the unwanted number by yourself.