how to purchase bus ticket

I need to purchase bus ticket from Shinjuku Station to Fuji Subaru Line 5th Station in this July to climb Fuji Mount. I can see there is a climbing season bus in japan guide website. There are schedules and price there. But, I can't find how to purchase the ticket. Please help. Thanks!

The timetables for the buses to the various 5th stations have not been published for 2025 yet!
Tickets for the buses from Shinjuku can be purchased here:
https://www.highwaybus.com/gp/inbound/index?lang=EN