Unable to connect to Raspberry Pi3 by hostname from Android VNC Viewer

1. I installed **VNC Viewer** on my **Ubuntu** from here. Then, I could connect to my **Raspberry PI** by both hostname and IP address. 2. However, I can't do the same from my **Samsung Note 8** I can't connect by hostname - I'm getting something like "Cannot resolve hostname". If I use the IP address then I don't have any problem. **Ubuntu** PC, **Samsung Note 8** and **Raspberry PI3** are all connected to the same WIFI network. Can someone explain what is wrong here?