Android Studio - NoClassDefFoundError: Failed permission of Landroid / support / v4 / print / PrintHelper

Question

I am trying to create a plugin for Unity3D using Android Studio.

I can show just a toast using this plugin, but I can’t work with the printer service.

This is my code:

void PrintThis(byte[] data){
    Bitmap bm = BitmapFactory.decodeByteArray(data,0,data.length);
    PrintHelper helper = new PrintHelper(UnityPlayer.currentActivity);
    helper.setScaleMode(PrintHelper.SCALE_MODE_FIT);
    helper.printBitmap("test print",bm);
}

When I call this method, I get the error message: NoClassDefFoundError: Landroid permission failed / support / v4 / print / PrintHelper

What am I doing wrong? I am testing an Android 5.0 device (printing requires API level 19)

Thanks.