Allow business owners to set a capacity on Price Bands

At present, capacity is set per session. All Price Bands that can be honoured are displayed until the session capacity is hit.

Sometimes, certain Price Bands/Ticket Options have limited availability. e.g. 3 Drop Ins per session.

This feature would allow a capacity to be set for that price band so it will no longer be offered when the Price Band capacity is hit for that session - even if the overall capacity still has space.