visitorId property

A unique identifier for tracking visitors.

For example, this could be implemented with an HTTP cookie, which should be able to uniquely identify a visitor on a single device. This unique identifier should not change if the visitor log in/out of the website. Don't set the field to the same fixed ID for different users. This mixes the event history of those users together, which results in degraded model quality. The field must be a UTF-8 encoded string with a length limit of 128 characters. Otherwise, an INVALID_ARGUMENT error is returned. The field should not contain PII or user-data. We recommend to use Google Analytics Client ID for this field.

Required.