I once had a kratom tree I kept inside an aquarium with a lid, so as to keep up the humidity and temperature. It grew quite quickly at first, but after about 3 weeks or so of arrival, growth completely halted. I kept it around for a while, trying to increase temperature and humidity, but I hadn't considered the air exchange.
The leaves started falling off, and it refused to grow. Eventually all the leaves fell off and I decided to take a cutting, thinking maybe it could regrow its roots, as if that were the problem. It turned out a fungus has colonized the entire inner bark, and there was no hope for it.
It doesn't seem to mind low humidity nearly as much as cold. It seems to grow a little slower in cold weather, but my Rifat grew well even at about 60F with a big LED grow light.
If you have the correct climate (ie Florida or similar), this should be a pretty steady plant. Maybe just a little more touchy than caapi.
If indoors, just make sure you have the correct space and setup.