Returns the campaigns assigned to a spend cap.

By default, when neither effective_at nor effective_from is set, the response includes every assignment that is active today or scheduled to start later. "Today" begins at 00:00 in the platform's time zone.

• Set effective_at to see the assignments that were active at a specific point in time.
• Set effective_from to see every assignment active on or after a specific point in time, including assignments scheduled for the future.
• If you set both and effective_at is earlier than effective_from, the response combines both: the assignments active at effective_at, plus every assignment active on or after effective_from.