Why doesn't my decal show up?
A decal's ID and its image's ID are different numbers. If you paste a decal ID into an ImageLabel's Image property in Studio, Studio converts it to the image ID for you. If you set it from a script, you need the image ID. The easiest way to get it is to paste the decal ID into the property in Studio once and copy the number it changes to.
Place ID vs universe ID
The number in a roblox.com/games/… link is the place ID, which TeleportService uses. The number in a Creator Hub dashboard link is the universe ID, which Open Cloud and some web APIs use.