In your SMS flow you can log information related to the sent messages; i.e. the notification, received from the SMS gateway, about the SMS status is logged in the database.
The notification messages have a priority lower than the Inbound SMS received by the Platform Server; therefore when the system is loaded the processing of the notification messages might take longer.
The behavior that OutSystems Platform has when the SMS gateway notification arrives can be configured at the:
eSpace level: the eSpace has a property where you can specify the behavior. By default, this configuration is used by all the SMSs. How?
Besides this, you can also specify the behavior that your eSpace must execute when the SMS gateway notifies Service Studio about the status of an SMS. This is done using the OnDeliveryReport system action. How?
eSpace Properties | Send Message Properties | Start iSMS Properties | OnDeliveryReport System Action