CAUTION ! the second link is for HOMOEOPATHIC medicine!
This means it is 99.9999 something other than the stated axtive ingredient and is therefore entirely useless, except for the placebo effect.
You can tell if it's homoeopathic because of the little 6X after the ingredients list.
e.g. the melatonin tablets in question states;
Ingredients:
Each Sublingual tablet contains:
5mg Melatonin (N-acetyl -5-methoxy-tryptamine) 6X
That little 6X means the active ingredient (melatonin) is diluted 10:1, SIX times over before it is put in the tablet.
So the active ingredient is 5 milligrams divided by 1 million.

You might as well suck on a stick of chalk.

Some homoeopathic medicines have dilution rates so high that the mathematics would indicate that there cannot be even one molecule of the active ingredient in them.

Strangely enough, melatonin is not on the controlled substances list and yet most chemists will not sell it unless under a doctors prescription.
It is a completely benign substance and should be freely available.
In America it is.
Although so are guns

so I spose that doesn't count for much.

Thorne Research inc make the genuine stuff and sell it in a range of strengths.
Start with the Melatonin 3 (3mg) and see how that goes.
You might have to hunt around for them.