Gets contacts who are opted into a given preference and a given address book
This operation returns an array of up to 1000 contacts who are in a given address book and who are opted in to a given preference.
If no contacts in the given address book are opted in to the given preference, an empty array is returned. Otherwise an array containing contact objects is returned.
Results are returned only for preferences, not preference categories.
If you specify the id of a preference category in the path parameter, an empty array will always be returned.