reservation: Shirakawa-go to Takayama?

I have been searching for awhile with no success. Spending the night in the area and cannot find a way to reserve a seat from Shirakawa-go to Takayama on the first bus out. The Nohi / Japan Bus Online reservation sites only seem to offer reservations from the cities to Shirakawa-go. Am I missing something, or are return trips first come first serve, pay when you board? Thanks.

Did you see the website below?
https://www.nouhibus.co.jp/route_bus/takayama-shirakawago-line-en/

Yes, but I did not dig deep enough. Thank-you for directing me.

I don't see anywhere to reserve a seat at that URL?

How to book:
https://www.nouhibus.co.jp/highwaybus/kanazawa_en/
Takes you to
https://japanbusonline.com/en/CourseSearch/11900040002

I've been to the Japan Bus Online site but could not find the right option. But I just figured it out - maybe this will help a future reader.

When selecting the Kanazawa --> Takayama direction, there does not appear to be a way to book from Shirakawago itself. The only departure options are Kanazawa and Toyama. But if you pick one of them, there is then a radio button to actually choose Shirakawago as the real departure bus stop.

Last link of JCT brings to booking, and if you click on option with arrival point Takayama, system lets you to choose Shirakawa-go as departure point.
However when we did the trip, then booked Kanazawa-Shirakawa, but Shirakawa-Takayama was without. Was quite many people (afternoon), but they gave 2 busses on same scheduled time so probably they know the situation:)

You can just call there. Tell them your name,bus departure time and your phone number.
Then they will give you your confirmation number.
You can pick up ticket before departure and pay for the fare on or before the departure time.

■Telephone reservation
1)Nohi Bus Reservation Center
　（9:00am〜6:00pm）TEL (0577)32-1688
2)Hokurikutetsudou Reservation Center
　（9:00am〜6:00pm）TEL(076)234-0123

I've never used the Nohi bus on that section, despite countless visits to Shirakawa-go, but I have found their service pretty good on the other routes I've used with them - those were all non-reserved (not able to be reserved) options.