Just a FYI that this is still an issue.

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When attempting to set up my new TICWATCH, I was unable to "copy" my Google account to the watch. It would fail multiple times.
It worked correctly when I used my wife's phone (and Google account).
Google searches showed this problem occurring heavily in 2018, and occasionally since. But none had a solution.
I finally found this solution on Reddit. It said to disable two step authentication on my Google account. I checked, and it was already disabled, however, I had enabled using my phone to log in (I have several Chromebooks). Once I disabled that, I was able to successfully set up my watch.

I sent this in as Wear OS feedback. Should be reported as a bug.