Within the permission wiki there is a permission called "essentials.pay.multiple" keep in mind, this is part of the old essentials wiki. Not essentialsx documentation. So it may no longer be present. However, if it is. How would I use it?

EssentialsX is a fork of the original Essentials. This fork aims to expand upon the original feature set, if something is removed (which i cant recall off the top of my head), there will be a good reason for it.

Okay, but any idea how I would use it in a command?

You can use * for wildcard. And the rest is done by Bukkit's Server#matchPlayer method. If you're not technical and able to read Bukkit's code I could not tell you exactly what the criteria is. But the gist is that if, for example, you don't complete a name it will match multiple people that have the given search term in their name.