After installing the app, Please make sure you have given necessary app permissions

In case you haven't given necessary permissions and would like to enable it, Please follow the steps as mentioned below:

Go to Phone Settings--> App Management--> App list--> Choose Fliptalk--> Permissions --> Allow permissions 

In case notification is not working after giving necessary permissions

In case notifications are still not working after giving necessary permissions, Please clear data or cache of your app. Follow the steps as mentioned below to do the same:

Go to Settings--> App Management--> App list--> Choose Fliptalk--> Storage usage--> Clear data and Clear Cache