Apple Watch software update 9.3 fails to download

Any error messages given?

If you see 'Unable to Verify Update' when updating Apple Watch - Apple Support

Your Apple Watch and iPhone are both being charged and connected to Wi-Fi?

...

Next, check these things:

1. Make sure that your iPhone is updated to the latest version of iOS.
2. Make sure that your Apple Watch is at least 50 percent charged.
3. Make sure that your iPhone is connected to Wi-Fi.

Keep your iPhone near your Apple Watch throughout the update. It could take from several minutes to an hour for the update to complete, so you might want to update overnight or wait until you have time.

...

copied from: Update your Apple Watch - Apple Support

I am also seeing this, repeatedly, on my Apple Watch Series 6. I have confirmed all of the above: my iPhone 13 is at iOS 16.3 (20D47), my watch was 95% charged when I started (I have also tried with the watch on its charger) and the iPhone is connected to WiFi. My watch is model MG133LL/A and is currently running watch OS 8.5.1 (19T252). It is showing 25.17 GB of memory available. When I try to update, I get the "Estimating time" and "Downloading to watch" messages for about 10 minutes, then the download fails.

Same problem here

Same problem here