IMPORTANT! This issue was maddeningly frustrating until I figured this out. I tried the restarts, deleting the app and reinstalling it, signing out of iCloud and signing back in, all of that. Yes, I had the Home app on my phone and my iPad, BUT when I clicked on the little house in the top left-hand corner on both the phone and iPad and selected Home Settings, BEHOLD! I realized they were not using the same account. They both had the same email address, but did not seem to be logged in in the same way. So I uninstalled the Home app from my iPad, signed out of iCloud, signed back into iCloud, reinstalled the Home app, and it immediately paired with my watch and worked like a charm. THIS IS THE ANSWER!!! Hooray!!!