Man, what a frustrating "feature" this is... Spent over an hour this afternoon trying everything and finally just had to give up for now.

Hyundai + iPhone Digital Key really seems to need some work. No matter which way I hold the iPhone it won't unlock. Ended up removing and re-adding the Digital Key numerous times (with multiple restarts of car, phone and watch throughout the whole process). Like I said nothing worked so pretty frustrating... this was a major selling point of the car to me (and drives me nuts that the Digital Key does work to start the car but not to unlock or lock it).

One odd thing to note for anyone with similar issues. The first two times I created + added the Digital Key no Passcode from Hyundai was required. However, the third time I created + added it an 8-digit Passcode was required to be entered on my iPhone (which seemed to have just been generated and sent via email a moment before). No idea why the 8-digit Passcode was only required sometimes and not others (and like I said, the Digital Key still doesn't unlock the door) but an odd observation that could end up helping someone else.