Admin Route Override

I'm attempting to add a new Controller ction on the Order Controller.
It's not returning a view just adjusting the order and returning to the order edit page.
The link to call th Action is /Admin/Order/ShippingNotRequired/{id}

When ever I call this action it returns a 404 page not found error.

Is there something I need to overide in the routing somewhere to get this to work?

Sorted the issue.
Turns out it was the action I was redirecting to that was the issue. Because it didn't exist.