Trying to reference the server's character isn't working

This is the “run on server” event - it’s in the player character’s BP:

This is the On Activate event that’s being called:

If I hook up the “Get Player Character” node the event works as intended but obviously its target is the first character in the game - not the character that called the event. But if I try to use the “Sender” reference it fails to cast. What am I doing wrong?

edit: this also doesn’t work:

This makes me believe the problem is I can’t pass any reference through my interface’s parameters because if I use “Get Player Character” on the receiving end of the interface call, shown in picture two, it does work.

Ok, this is OP. I fixed it, but I think this was a bug. Since I added an input to my interface’s function long after I created it I think it was just wanting to return None all the time?

I fixed it by simply deleting and recreating the interface’s function and removing and readding the interface to the target actor. Now it works with the exact same setup I had problems with shown above.