I just purchased a small serissa from Ontario.It was shipped to me in Nova Scotia.Received in excellent condition.I am growing this Bonsai under grow lights.The room is heated at 74 degrees and humidity is 68%.The tree is not dried out.After about 4 days the leaves started turning yellow and falling off.Does anyone have any suggestions as to what might be causing this problem.I am a beginner at Bonsai.

Perhaps share some photos as well?

Did you check the care guide here?

www.bonsaiempire.com/tree-species/serissa

I would think high temperature and low humidity is part of the problem.

Most likelly it was kept cool where you got it from and now it is confused about the season. Try to put it in a spot somewhat cooler. If you can get as low as 10c it is the best and no light is needed.

I thought I downloaded a picture.