I have had great success with this plant and have just found an interesting article on it that has surprised me, to say the least!
I was led to believe it to be very difficult and fussy in that it is SUPPOSED to be finicky about it's environment and many other things. I find it very hardy and easy with one exception. Do not under water it!! It does very poorly if left to dry out.
Here is the typical article you'll find on Serissa:
https://www.bonsai4me.com/SpeciesGuide/Serissa.html
Here is an article I've just been forwarded by a club member in my area:
https://www.bonsaimary.com/a-serissa-forest.html
This guy has kept his plants outside all Winter with great success. I live less than 60 miles from his location which is on the coast. They get only a slightly milder Winter than do we just a bit further inland. I will definitely be testing his theory out this coming Fall/Winter, giving some protection to the plants. I'm just amazed to find that they are even tougher and more Winter-hardy than I'd thought.
BTW, we've just had a cold snap here in Jersey since I put my Serissa out and they are flowering wonderfully and seem very happy with their new environment.