That’s exactly the idea behind the interfaces – you don’t have to cast. You can send an interface message to any actor, regardless anything. However, if you see the yellow pin in the interface call, it means you’re doing it wrong – maybe that’s why you can’t achieve what you’re trying to achieve?
You have to use your_interface_name (message), not your_interface_name (interface call). You can use Interface Call to call it within the same BP, but to communicate between different BPs, you have to use Message.