Nothing deceptive about Melatonin being in the Relax gummies. Diamond's website list Melatonin as an ingredient in it. If they didn't list it as an ingredient, then THAT would be deceptive.
Also a fun fact about Melatonin, your own brain produces it naturally too.
When Diamond says there are no synthetic ingredients in their CBD, it means just that. Their CBD oils are extracted from industrial hemp and it's 100% natural CBD. There is no synthetic CBD in their products, but it doesn't mean that their products that contain natural CBD can't also contain other ingredients such as Melatonin.
Technically speaking though, simply extracting the CBD oil from the hemp or MJ plant is a synthetic process. So one can say all CBD extracts are synthetic.
By definition, “synthetic” simply describes a compound that is created using man-made force. And that compound may or may not be found in nature. Chemically speaking though, synthetic copies of natural compounds are structurally the same.