List of field values?

[MrBigmit37]

I am trying to a list of values for the show-fields index to see what's available.

I attempted something like this:

"https://content.guardianapis.com/show-fields?api-key=xxxxxxxxxxx"  (xxxx = api key)

However I get back a status failed.

This type of url worked with tags and sections.

Thank you.