Dynatrace collects a multidimensional baseline for application and user action traffic and therefore learns the typical traffic pattern of all your applications and user actions.
Abnormally low application traffic can indicate full application outages, so alerting on abnormally low application traffic is enabled by default.
In the Dynatrace menu, go to Settings > Anomaly detection > Applications to adapt the sensitivity of low-traffic alerting. When enabled, Dynatrace follows a time-interval comparison pattern (daily or weekly) in alerting on abnormal traffic situations. The actual monitored application traffic is compared with the previous interval and alerts if the comparison reports unusually low traffic.
You might be able to get the threshold values via the API