I need support with the development of a SDK that runs within the Unity for Android games

I need support with the development of a SDK (or package) that runs within the Unity for Android games, this SDK need to open a browser and perform some procedures, after using the SDK it has to send data to the Android application, then we need somehow execute the methods defined in android code, within the SDK that is running in the browser within the game.

Problems encountered:

We are encountering a problem in the communication of Cordova Android WebView within the Unity. One problem is the implementation of methods defined in a JavaScript interface, the debug returns in the following message when trying to access the methods:

Error calling method on NPObject.

Another problem found, is to close the current activity after opening with unityPlayerActivity.startActivity (...).

The UnityPlayer.currentActivity.onBackPressed () method and UnityPlayer.currentActivity.finish (); does not work.