Transmitting the site user ID set by the site owner.
ym(XXXXXX, 'setUserID', "12345");
XXXXXXis the tag ID.
12345is a string value.
Your website user ID is associated with the ClientID of a particular user only if the setUserID method was called during the user's session.
Note. To see UserID values in reports, transmit them using user parameters.