setExternalId
Assigns a unique identifier to associate the currently tracked Klaviyo profile with a profile in an external system, such as a point-of-sale system.
NOTE: Please consult (documentation)[https://help.klaviyo.com/hc/en-us/articles/12902308138011-Understanding-identity-resolution-in-Klaviyo-] to familiarize yourself with identity resolution before using this identifier.
The SDK keeps track of current profile details to build analytics requests with profile identifiers
This should be called whenever the active user in your app changes (e.g. after a fresh login)
Return
Returns Klaviyo for call chaining
Parameters
externalId
Unique identifier from external system