Why is my event showing 'Not Open Yet' on the event ticketing page?

If the event is a series (of events), and is not open for sale yet, the event will show NOT OPEN YET until the sale period starts.

The ticket type for the event will also show NOT YET, without any other information if the ticket sales period is not defined. If the sale period for the ticket type is defined then below the name of the ticket, the AVAILABLE FROM tag will show the start (and end, if provided) date and time of the sale period.

If it is a single event, only the ticket type will show NOT YET as described above.