Hi,
I'm an official rep. from Viber. I'm here to help
First, please make sure that you have the latest version of Viber installed.
Also, if you are using a Custom ROM - do you know whether or not Viber worked when your phone was on Stock ROM?
If the problem still persists, then we would appreciate if you could take a minute and report the details to our support team using this direct link:
Your ticket details
When you submit the ticket, in the line called: "Through which channel did you submit your initial inquiry", please make sure to choose "Technical Forum". With this information, our development team will hopefully be able to find the source of the problem, and ultimately resolve it.
Thanks in advance