Overnight ferry between Osaka and Beppu

Planning to travel by Sunflower ferry. How can I book tickets in advance?
I tried through the official website-it is not working (even when I see availability, there is not possible to continue)
By phone ,the number provided is only for domestic calls.
I could not find any email address even if the web indicates that bookings can be made through email.
Maybe a travel agent could help?
Thank you

You can book 3 month prior to your departure and email booking are accepted .
You might be trying to book too early perhaps?
I used Sunflower Ferry, between Osaka and Shibushi this October. I had to wait until the day I could book. However I made my booking on Japanese website.

I tried for the period open to sale.
Can you give me the email address,I couldn�ft find it in the website.
Thank you

I tried through the official website-it is not working (even when I see availability, there is not possible to continue)

This website? https://www.ferry-sunflower.co.jp/en/
I can see the reservation form (where you input your name & passport number) after selecting the room.

I tried for the period open to sale.
Can you give me the email address,I couldn�ft find it in the website.
Thank you

sunflower-fs@molgroup.com
I do not know whether they answer your email. This is not for booking but they might answer your question. Good luck.

Thank you all.
Yes, that website.
Unfortunately I cannot see any reservation form because on the screen appears :
"We are sorry, but reservation system is not available for maintenance".
Thank you for the email address, I will try to contact them.
I will also look for a local travel agency.

Ah, are you trying to make your reservation between midnight-5am JST (I'm getting that message right now as well)? It is quite common that Japanese websites are unavailable around that timeframe (for maintenance), and it looks like the Sunflower ferry is no exception.

Thank you, I did not know that about Japanese websites. I will try during Japan working hours.