Viber app doesn't make the phone vibrate when calls come through it

[Desiree]

I recently downloaded the viber app and I've had it for a while but there's a problem that's been bugging me. Viber only vibrates when someone is calling me when my screen is unlocked. so everytime my screen is locked and a call iis coming through, it only says incoming call and it doesnt vibrate. how can i make it vibrate when calls come through on lockscreen? I always leave my phone on vibrate because that isnwhat i prefer.
Is there a way I can fix this?

 

[Raz0rEdge]

Perhaps I'm confused, but iOS will vibrate (and play music) on incoming calls automatically. Why do you need another app to do this work?