I have the credentials I need already set up

I want to bind a particular credential in one of my jobs so that the vars are available to shell script within it

The docs here https://support.cloudbees.com/hc/en-us/articles/203802500 say I need to:

1. tick "Use secret text(s) or file(s)"
2. add a binding of env var name to credential

When I try to do this I get the "Add" binding dropdown with options in it but nothing happens when I select any of the options

The UI to configure the binding does not appear