In October 2017, we deprecated our iOS and Android native mobile apps as announced at https://status.serverdensity.com/incidents/646l5v84ctns - the apps were removed from the app stores but push notifications continued to work.
The primary use case for the mobile apps is receiving alerts but we have found that most customers are using 3rd party alert notification systems such as Slack, PagerDuty, VictorOps or OpsGenie. These products all have mobile apps and analysing the usage of our apps has shown us that they are not widely used and usage has been decreasing even whilst we were actively maintaining them. We also provide a free SMS alert quota for every account which is an alternative to push notifications to our apps.
As of 2018-10-03, push notifications will cease to function.
In the coming weeks we will remove the ability to choose push notifications from the product UI and API and automatically migrate any configured alerts to email. Any affected users will be notified via email about this change.