# Why do I get duplicate events?

If you're getting duplicated events when you edit existing events, it may be because of how you're using `event_id` and `event_uid` values.

Cronofy operates an *upsert* model when creating or updating events from your application. The API creates an event if one doesn't exist or updates an existing one if it does. The key field used to identify an event from your application is the `event_id`. This is a value that your application specifies and manages.

The most common cause of duplicate events is using the `event_uid` value in the `event_id` attribute when attempting to update an event.

An events `event_uid` is Cronofy's internal identifier for the event. The reason there are two IDs is because we differentiate between events that your application *manages* and events that are created in the calendar by other means, eg by the user. We call these *unmanaged* or *external* events.

You can only use the `event_uid` to edit *unmanaged* events. This requires and additional permission from the end-user before you have this capability enabled. See [Edit External Events](/developers/api/events/edit-external-events/index.md) for more information.


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