Certified GKH Gardening Expert
This is a sign of a pest infestation. The glossy film is honeydew. Check the undersides of leaves and where the stems meet. There are several that it could be and, fortunately, they are all treated the same way.
Treat the plant with a pesticide. I personally like neem oil, as it is safe for people and pets. Here is more info on it: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm