Magnesium can promote sleep through multiple mechanisms, though it typically does not treat insomnia directly.

“the evidence by way of you've heard the story of that magnesium is good for sleep it's principally derived from evidence of people who are magnesium deficient and when you make them magnesium normative they start sleeping better that's a very different question than saying I am magnesium normative I am in normal ranges and then I add to it how do I expect any greater benefit”

“magnesium also does seem to promote sleep in a number of different ways actually more than just one way. Um, doesn't treat in doesn't usually treat insomnia, but it can help promote sleep.”