Dang! I missed the last couple new posts on this thread.. is it outside, yet?
You say that putting it outside was the cause of it’s problems.. or didn’t help it..
For “day 1” it should only be 1-2(max) hours of direct sunshine.. did you perhaps go longer..
Everything here.. including tender succulents, has been “out” for over 2 weeks... My serissas have been out longer, actually.. they “move” with ficus and punicas, in my routine.
My observations from the first two Serissas that I killed, lead me to believe that.... they use the summer months to recover from the “indoor hell” (to a plant) that IS an uncontained, SEMI-controlled indoor area. My Serissas grow very well indoors.. now. In my FIRST two “grow situations”, they limped (actually even decline sometimes in Autumn) all winter to TRY and bounce back in summer... One died... then the “acid-water fiasco” killed the other.
The live ones I have now do well.. but I believe both Experience and a more-efficient-than-last-time growing area are to blame.