Customer User ID field (CUID)

At a glance: The CUID enables you to group events of the same user across different devices, applications, media sources, or channels.

What is CUID?

The Customer User ID (CUID) is a unique user identifier that the AppsFlyer SDK can add to install and in-app events. Using the CUID, the events can be cross-referenced with user data extracted from other channels.

Why use CUID?

The CUID enables you to group events of the same user across different devices, applications, media sources, or channels.


A user with two or more devices has the same CUID. Each time the user performs an event on a mobile or desktop device, the event is captured along with the CUID. This enables the advertiser to combine the devices' data into a holistic user view.

A few use cases:

  • In-app purchases performed by the same user on multiple devices (phone, tablet, TV, desktop) can be combined in a single view.
  • User performance in a game installed on multiple platforms (desktop, mobile, TV) can be shared across platforms.

Setting the CUID

It's recommended to set the CUID before calling the start method, which sends the install event to AppsFlyer. 

Set the CUID in Android

In Android, the start method and CUID setup can be executed from either the global Application class or an Activity class, depending on the app implementation. For more information, refer to Select in what class to start the SDK.

Set the CUID in the global Application class

If you want to associate the CUID with the install event when starting from the global Application class make sure to delay sending out the install event using the waitForCustomerUserId method. This method puts the SDK on waiting mode until the CUID is set.

Note: If for some reason setting the CUID fails, the SDK will stay in waiting mode and not send out any events.

Set the CUID in an Activity class

When the SDK starts in an Activity class you don’t have to delay sending the install event. Simply set the CUID before calling start.

Developer Instructions

Inform the developer of the following:

Set the CUID in iOS

Use the customerUserId method to set the CUID. The location of customerUserId  in relation to the start method determines what events can be associated with the CUID.

  • If customerUserId is called before calling start, the CUID is associated with the install and the following in-app events
  • If it is called after start, the CUID is only associated with events recorded after setting the CUID.

Developer Instructions

Refer the developer to the following links:

CUID and privacy

AppsFlyer values and respects the privacy of you and your users and doesn't permit the collection or transfer of directly identifiable personal information to the AppsFlyer platform.

To secure the privacy of your users, design the CUID without information directly identifying the user. For example, it should not contain an unencrypted form of the user's email address, name, telephone number, or social security number. Any sensitive information included in the CUID must be encrypted.

Further reading

See User journey reports to learn more about the CUID in raw data reports.