You can configure monthly data limits in the UI, within the Service Profile configuration. Once the data limit is exceeded by an endpoint (which has that service profile assigned), the PDP Context is rejected and an alarm is displayed in the UI.
If you would like to define a daily data limit, you can use the API Quota Management (you can also set an expiration date). It is also possible to define an action to be performed on the expiration date, i.e. the endpoint can be blocked for data services or merely see the connection throttled.
The daily limit will auto-refill everyday at midnight UTC until the expiry date is reached.