Cinnamon trees are prone to root rots if over-watered or the soil too moisture retentive. Use a good quality, fast draining potting soil and only water when the top inch of the soil is dry (or you lift the pot and it seems very light). Then water thoroughly until the water runs freely from the drainage hole and don't water again until the soil is dry. It also need some bright light - sunlight preferred - so try placing it on a window sill. And the tree prefers somewhat acidic conditions, so fertilizing with something formulated for acid lovers (i.e. MirAcid) would be helpful.

I am not sure the best soil requirements but if water retention is an issue maybe try a 5-1-1 or 1-1-1 gritty type mix?