Watchos 9.3.1 won't download

I've been trying to update my Apple Watch Series 8 to Watchos 9.3.1 for a couple of days now, with no success.

Each time, I get prompted for my passcode and enter it, then "Estimating Time Remaining" shows for about 15 minutes, followed by "Software Update Failed" dialog.

Yes, watch is on same WiFi as iPhone, close proximity, and no other obvious connectivity issues. I looked for an old "Software Update" file under General>Storage and found nothing.

Any ideas?

Thanks!