I have a list of Providers:
The "Provider" field is the Title field.
Then I have a Tickets Category field:
The "Provider" field is a lookup to the "Providers" list. The "Category" field is the Title field.
The "Tickets" list has a "Provider" field and a "Ticket Category" field.
I setup the "Ticket Category" field to be filtered by the Provider field. I think it is all setup correctly, but the filter isn't work.