If your garment has zippers, the sliders, pulls or the entire zippers can be replaced with a lockable version.
Works if you have two sliders.
Sliders with hasps
Also two sliders are needed. Hasp sliders/zippers are the easiest to find and the most secure/reliable solution. Such zippers are used in, for example, backpacks and bags.
Hasp sliders by Ansun (search for “pad lock”)
Key lock sliders
The most invisible and discreet way.
See what’s available on eBay.
See also: Schlumbohn-Grabotex