Great question! You have to email them & prepay or just show up.
Here is their website: refuge-orisson (sorry I can't put the website in my answer, but you can get it).
There is a contact us button.
Hope that helps!
We booked online. It took a couple of days for the answer to come.
Or you can use the contact form on their website - just google it, I cannot post it in my answer apparently.
The phone numbers are there also if you are local.
I hope this helps
Get an answer from Refuge Orisson staff and past guests.