I registered a Facebook Account just to see my Instagram Followers on LaMetric. I linked the Facebook Account to my Instagram Account. Then I tried to link the LaMetric App to my Facebook Account but all I get is:
OAuthSwitftError-Error -5 "serverError[access_denied]"
I tried it multiple times, even deleting the Instagram App from LaMetric and reinstalling it. It just does not work.
Nevermind, as it seems you need to wait some time after you created and linked your facebook account to your instagram account. It works now.