Step 1:

Download and install Wi-fi Messenger app on both devices. To download app from playstore click_here.

Step 2:

Connect Both Mobiles with Wi-fi and Hotspot

Example:

Step 3:

Open Wi-fi Messenger app in both Mobiles.
Then click on button in both mobiles and wait until the connection is done. And after Connection Successful, start chatting.

Option 1:

Update your app if you are using older version. And try to connect.
click here to update your app

Option 2:

start the server first, and then start the client

even after that, there is problem to connection,
start the server in any one device. And in another device, try to connect using ip address of server

Option 3:

In case, connection is not Successful, try to swap Wi-fi - Hotspot connection and try again.

Example: