I just updated the plugin by using the one in the Amazon mobile app SDK, plugin v2.4.0.
In AmazonGameCirclePluginVersion.txt, it states - Adds the AGSignedInListener callback interface. You can use this to detect when the signed in state of a player changes. - Adds the PlayerClient interface, which retrieves player information for a given player from the Amazon Game Service. This interface provides the isSignedIn and setSignedInListener methods that you can use to check and detect the signed-in state of a player. PlayerClient replaces ProfileClient.
I do not see AGSignedInListener, PlayerClient.isSignedIn nor PlayerClient.setSignedInListener. Am I missing something?