Taking airbus from Taipei to CKS airport

I already know where I can go to catch the bus.

My question is: Do I need to purchase a ticket in advance at some inconvenient Airbus office location, or can tickets be purchased upon boarding the bus?

Tried to check their website, but it comes out in jargon (even though I have the Chinese language pack installed on my computer).

You buy them when you board the bus.
From the airport you may need to go to the little booth at the bus stop.

Take Boeing instead. Refuse Toulouse.