Trouble with configuring a custom input validation

Hello,

Does anyone have experience with setting up custom input validations? From what I've read it looks like I would just need to configure a system filter and then select the filter from the input validation dropdown, but my filter is not appearing in the list of available validations. Would I need to do anything else aside from creating the filter in order to make it available as an input validation option? 

Here is how my filter is currently configured:

and this is where I'm trying to select it from: