Answer by Graham Dunnett

The typical problem here is that you've called `initPlugin`, and then instantly called `SendMessage`. The docs at: http://docs.unity3d.com/Documentation/Manual/UnityWebPlayerandbrowsercommunication.html recommend that you wait for the game to load before trying `SendMessage`. One way to handle this is to have your `InstagramManager` object call out to the HTML JS when it starts up, using `Application.ExternalCall()`. The function in the HTML JS that you call can then use `SendMessage` to talk back to the Unity script, and pass in the access token.