I haven't used Apple Pay yet with the X. We set up cards on the device during set up assistant, put in the security codes etc., then today at the Apple store it wouldn't work. Turns out after the 11.1 update and/or restore, the cards were gone. Had to re-add them but haven't been out since.
I used the phone for Apple Pay more than the watch since the phone will light up if the terminal is accepting NFC. Otherwise, you look like an dummy holding your watch over the terminal wondering if it works or not.