UUID (Universal Unique Identifier) is a unique string of up to 64-characters that is used to identify a client (end user, device or server) that connects to the PubNub platform.
It is required to pass a UUID when you instantiate a PubNub instance (i.e. new PubNub()). UUID should be persisted, and should remain unchanged for the lifetime of a user or a device that connects to PubNub. You can accomplish this by either passing the UUID to the client upon successful login or by persisting the UUID on the client where it can be retrieved the next time the PubNub instance is instantiated.
If you don't set a UUID yourself, PubNub SDK generates it randomly for you. So it is important that your application re-uses the UUID on each device. Not setting UUID explicitly can have significant impact on your bill if your account is setup with the Monthly Active Users (MAUs) based pricing model. If you have enabled Presence for your key set, not setting a UUID that is consistent for an end user may result in unexpected presence behavior.
Please, refer to the following documentation for more information about UUID configuration:
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