Properties of the profile that triggered this event. The profile must contain an
identifier. The $email and/or $phone_number can be used as the identify the profile.
Other key value pairs can be used to create segments. For example, to create a list of
people on trial plans, include a profile's plan type in the profile. The profile
supports special fields. The fields include: $email (string), $first_name (string),
$last_name (string), $phone_number (string), $city (string), $region (string; state or
other region), $country (string), $zip (string), $image (string; url to a photo of a
person), and $consent (list of strings; eg: ['sms', 'email', 'web', 'directmail',
'mobile']).