If you see that there are no messages in the WhatsApp menu, you can check the following things:
1. First of all, read this article about all the general reasons for no data in your control panel.
2. Check if the target device is rooted
This condition is for Android OS only
Some features such as WhatsApp tracking (or other social networking applications) needs the device rooted.
You can read what feature need the phone rooted.
You can read an article about how to root an android.
3. WhatsApp has some different versions
There are different methods to encrypt and read the messages from WhatsApp application, so please tell us about the version number of WhatsApp installed on the target device. Our developer team will try to install the same and will open investigate on this to make it works better.