why i cat see message alert and number of message against contact name in viber in lumina 430

[Windows Central Question]

i just buy lumina 430 and set up viber , but in it when any frnd send msg on viner it shows in the top bars or screen but when i go inside viber contacts there is no alert or notification against the name.. so i dont know who have send the msg. how can i update this feature in lumina 430, thanks to help