The vanity code is the text that shows to the right of the domain of your link.
Vanity codes can only be selected during link creation. Once a link has been created, it’s not possible to make any changes to its vanity code.
If you do not designate a custom vanity code when creating a new link, a random string of letters and numbers will be used instead.
If you like your vanity code, you can always update the destination on your link--or change the link’s type--and use it for something else.
Or, if you ended up with a vanity code you don’t want to use, go ahead and create a new link!