# On App Trigger

> The **On App Trigger** starts the process execution as a response to an API event. It leverages Event Triggers from Integration Service, Microsoft 365, Google Workspace, or System activity packages.
:::note
The **On App Trigger** event corresponds to the **Message Start Event** element in BPMN.
:::

The **On App Trigger** starts the process execution as a response to an API event. It leverages Event Triggers from Integration Service, Microsoft 365, Google Workspace, or System activity packages.
:::note
The **On App Trigger** event corresponds to the **Message Start Event** element in BPMN.
:::

Use **On App Trigger** when developing automations triggered by external events, such as email actions, items added to queues, employees created in Workday, or records created in SAP.

![docs image](https://dev-assets.cms.uipath.com/assets/images/activities/activities-docs-image-523268-70d787fb.webp)

To start the process any time an external event occurs:

1. Right-click on the **Manual Trigger** or the **On a Schedule** canvas element.
2. Select **Change Type**.
3. Select **On App Trigger**.
4. Right-click on the **On App Trigger** canvas element and select **Set trigger**. This opens the list of all available API events. If the API event you selected is not installed on your device, you must wait until the installation of the container package completes.
5. Once selected, the **On App Trigger** is replaced with the corresponding activity.
6. In the properties panel of the API event, provide the values for the conditions under which the process must start executing.

    For example, if you selected the **File Updated** trigger, you would need to provide values for the **File Updated** activity in the Microsoft Office365 activity pack.