Can you please explain exactly how to check for a duplicate as someone types into the form. I can validate on submit, but want to check a particular field as the user types.

Hello Bobby,
Server-side validation is executed only on running the server action.
You can use the condition step in server connect in order to check if a filtered query returns records, and if yes - you can show/hide some container on your page (for example saying "Duplicate found" ).