Cancel the scheduled message

delete https://sms.8x8.com/api/v1/subaccounts/{subAccountId}/messages/{umid}

This resource can be used to cancel a scheduled message that has not been sent yet using the unique message identifier (UMID) of the message.

URL

You need to specify the sub-account id and the umid of the message in place of {subAccountId} and {umid} respectively.
umid is the unique identifier you received when you submitted the message to the API.