Are you sure?
What is rattan rope? Rattan is by definition flat since it's the peeled outer layer of whatever plant it comes from. I've woven a lot of chair seats of various kinds and have never come across anything called rattan rope. Not that that means it doesn't exist!
That chair is woven with...
That chair is woven with binder cane. Most likey it's 5mm binder cane. If you are doing it yourself soak the cane in COLD water not hot, lot's of internet sites recommend hot water (hot tap water) but that can discolor the cane (goes dull and greyish). Cold works perfectly!