For anyone using NatWest in the UK and running iOS 26 B4 as well as watchOS 26 B4, I had a strange bug adding my NatWest debit card to the watch. Whether this is a bug caused by iOS 26/watchOS 26 or a buggy app, I'm not sure, but I have an easy workaround.
On the phone I could add my debit card and verify it ok, but on the watch app on the phone I could add the card but the NatWest app would refuse to verify it and give me an error saying we can't verify it at the moment. And tapping the verify by phone does absolutely nothing.
Easy fix, remove the NatWest card from the iPhone wallet and watch wallet, open the NatWest app and add the card to the watch wallet first this way only. This adds the card and verifies it all in one go, then just tap the button underneath your card in the NatWest app to add the card to the iPhone wallet after the watch is done, did it this way and both cards work great. Strange bug, but at least it's an easy fix if anyone happens to come across this issue.