There is known issue where adding devices to ObiTalk works "intermittently". Poly is aware of the issue, but has not given an ETA (although it has been going on for some time).
Since the feature sometimes works, the best advice thus far is Keep Trying
Some other user advice (though unconfirmed) has been to uncheck "Add Google Voice" before starting the process and to do it in "off hours" - Per Poly, It's the same site and servers used world wide, so not sure how that last one works.
In Early January it took several attempts for me to get my 212 connected, but got it working afeter continually trying for about a half hour at 1:30am in the US. More recently, I have ben trying to add a 202 over the last few days to no avail.
The steps you are following are correct - it is the "intermittent" issue that is most likely keeping your device from registering.
Good luck.