Kyoto to Fujikawaguchiko?

We want to stay overnight in Fujikawaguchiko, after a lot of research, the best way to go is to ride a Hikari to Mishima station and then take a highway bus to Fujikawaguchiko. But I've tried reserving a bus ride on the sekitori website. It says service requested not found. This is our first trip to Japan which is in April and I'm not confident in how to get to there. I've seen options such as going to Tokyo and then heading to Fujikawaguchiko but I'd like to go the fastest route. Is the booking the highway bus a user problem that I'm encountering, am I booking too early? Or am I on the wrong site? Can someone explain to me with more details as how I can prepare this.

Reservations are doable but it is too early as you suspected. Further info on the site says reservation open one month before the boarding date.

Bus reservations won't open up till a month from departure date.

Thank you guys for answering! I might be over-worrying a bit to early!