Segments
A segment is who a group-scoped event is about. A static segment keeps a list you add to; a dynamic segment holds whoever's attributes contain its filter, so nobody keeps it up. Beside the segments somebody keeps are temporary lists, picked by a person for one send: you can see them, but a key cannot change one and an event cannot name one. In the Subscription business pack a segment is, for example, “Annual plans”.
GETList who is in a segment
Requires groups:read. The subscriptions a static segment lists — or customers, for a segment of customers — whole. A dynamic segment keeps no list, and an empty one here would read as “nobody is in it”, so it is refused: ask /matches.
200 with an array of subscriptions or customers. 400 on a dynamic segment.
A bare JSON array. Each item is one subscription: the same fields in every pack. Press Response on the sample to see one whole.
On failure the body is { error, code } instead.