@Override
    void assembleMessageParameters() {
        MeshLogger.verbose(TAG, "NetKeyIndex: " + mNetKey.getKeyIndex());
        MeshLogger.verbose(TAG, "AppKeyIndex: " + mAppKey.getKeyIndex());
        final byte[] netKeyIndex = MeshParserUtils.addKeyIndexPadding(mNetKey.getKeyIndex());
        final byte[] appKeyIndex = MeshParserUtils.addKeyIndexPadding(mAppKey.getKeyIndex());

        final ByteBuffer paramsBuffer = ByteBuffer.allocate(3).order(ByteOrder.LITTLE_ENDIAN);
        paramsBuffer.put(netKeyIndex[1]);
        paramsBuffer.put((byte) (((appKeyIndex[1] & 0xFF) << 4) | (netKeyIndex[0] & 0xFF) & 0x0F));
        paramsBuffer.put((byte) (((appKeyIndex[0] & 0xFF) << 4) | (appKeyIndex[1] & 0xFF) >> 4));
        mParameters = paramsBuffer.array();
    }
Returns the application key that is needs to be sent to the node

@return app key
mesh/src/main/java/no/nordicsemi/android/mesh/transport/ConfigAppKeyDelete.java