API v 2.3.x is working great on android, in sdk sample there is App42_Unity3D_SDK_WP8_x.x.dll added, that's why you are not able to call any service on android, Because the WP8 _x.x.dll is only for Windows phone 8.
App42 Unity SDK consists of separate DLLs to be used for building on Windows Phone and is available under x.x/App42-Unity3D-SDK-WP8 folder of downloaded zip. However, for the rest of the platform it is available inside x.x/App42-Unity3D-SDK folder.
So just replace the App42_Unity3D_SDK_WP8_x.x.x.dll with App42_Unity3D_SDK_x.x.x.dll .