Where need to find the setUserIdentifier key?

[arishanapalli]

Where I need to find the setUserIndentifier key.
Crashlytics.sharedInstance().setUserIdentifier("12345")

No idea what need to place in place of "12345"?

[middlinp]

This is the same as it is in the Crashlytics documentation:
https://docs.fabric.io/apple/crashlytics/enhanced-reports.html#user-identifiers