That route is actually a on-demand bus route which you must book at least 4 hours in advance. Cost being NOK 64
To look at the timetables, you can go into the travel planner, enter your route, date and time and you'll see the services
You can then see it's a on-demand route. If you have a norwegian phone number you seem to be able to click on Bestill Snelandia Fleks (Book Snelandia Fleks) and book it online that way (untested).
If you don't, a message states you must call them, again at least 4 hours in advance
Plass må bestilles senest 4 timer før avgang. Tlf: 75 77 18 88. Advance booking required at least 4 hours upon departure. Call 75 77 18 88.
You buy the ticket for it on the app just before boarding the bus
Vi anbefaler at du kjøper billett på forhånd i appen Snelandia Mobillett, som alltid vil være det billigste alternativet. Billetten kjøpes på forhånd like før ombordstigning for å unngå at gyldighetsperioden går ut før reisen er avsluttet. Du kan kjøpe både enkeltbillett og periodebillett.
Google translate
We recommend that you buy a ticket in advance in the Snelandia Mobillett app, which will always be the cheapest option. The ticket is purchased in advance just before boarding to avoid the validity period expiring before the journey has ended. You can buy both a single ticket and a period ticket.