Takayama discounted bus fare at matsumoto

For JR east nagano niigaya pass

Takayama by bus from matsumoto
Do i need to purchase the discounted bus pass and book the seat prior to departure ?
Or reservation date is not mamdatory ?
Please advise

You must purchase it before departure. No reservation is necessary (after you purchase the ticket you can use any bus during the ticket validity period).

Note that it's a round-trip ticket, valid for 7 days.