I ran into the same problem on my new Galaxy Watch last week and read almost all related posts, but none of them worked. So, I want to share my solution, hope it helps you.
symptom:
When I added the Google account to the Galaxy Watch 4 when I set up the Galaxy Watch 4 for the first time, it could find my Google account and then started copying the data to the Galaxy Watch 4. But it took a long time, even I waited all night, and finally Failed.
Reason 1: Wear OS may not support multiple Google accounts.
Solution 1: Delete other Google accounts
This is the currently proposed solution. Because I also have two google accounts on my phone, I think this is the solution I was looking for at first. Unfortunately, after I deleted the second account that I didn't use very often, it didn't work for me.
Reason 2: The data and cache of Google Play Store are too large.
Solution 2: Clean up the data and cache of the Google Play Store App on the phone
I think most people use their phones with Google Play Store App for a long time, so the data of Google Play Store becomes very large (about a few GB) and it takes a long time to copy the data to Galaxy Watch 4 and it fails at the end . After deleting all the data and cache of the Google Play Store on the phone, the account can be added to the Galaxy Watch 4 immediately. The data is automatically synced back to your phone from Google servers, so it is safe to delete it on your phone. The cache can be deleted at any time, and it will be automatically recreated when you continue to use Google Play. No need to log out of your Google account.
Please try to see if it works for you. good luck.
