redirect_uri_mismatch when using Google Analytics +

I'm trying to set up Google Analytics + on my site network. I have it network enabled. I click on "set up Google API project" as in your instructions. I enter my data in the 3 fields. I click Authorize, and I get this error from Google:
400. That’s an error.

Error: redirect_uri_mismatch

The redirect URI in the request,, does not match the ones authorized for the OAuth client. Visit shortened to protect code numbers)/ to update the authorized redirect URIs.

Learn more
Request Details

That’s all we know.

Any ideas what's wrong? I suspect it's the Request URL setting. Your instructions say:
"5. Important: Enter the URL of your primary network site in the field marked Authorized Redirect URL."
I entered "". I'm guessing there needs to be some path with it, but your instructions don't say which path is prepared to accept the callback from Google. Please advise.