Melatonin safe dose range per Drugs.com

5mg

https://www.drugs.com/medical-answers/melatonin-maximum-safe-dosage-3113942/

There is no official recommended maximum dose of melatonin for adults, but a range of 0.5 mg to 5 mg appears to be safe and effective.

Generally speaking, most people produce enough melatonin to sleep well, but if you need a little extra to add to their sleep cycle, you probably don’t need more than 3 mg.

Some people sleep better with as little as 0.3 to 0.5 mg. Melatonin is not regulated by the FDA in the US and is often sold as a dietary supplement and has not been subjected to the same safety or efficacy requirements as a medicine.

There are no regulated manufacturing standards for dietary supplements and some have been found to be contaminated with toxic metals or other drugs. It is recommended you purchase Melatonin from a reliable source to minimize your risk.

https://www.mitozen.com/product/super-sandman-high-dose-melatonin-bullet/

»Super SandMan™contains 450mg of Melatonin, Terpenes, a Proprietary blend of SandMan Complex™ along with our proprietary AP0-808™ probiotic strain.   There is a slow release over a 5-7 hour period, to support sleep all night long due to our proprietary slow release technology using SRT ™ Polysaccharide Complex.»