Viber wants to grow the community and help people to build a chain of members in one group. Therefore, it has now allowed the group members to add other members also.
Not only admin can add members rather other group participants can also add the member. For this open, the group chats, and here you will find the icon of the share. Tap on it and ad a maximum of members to the group.
It is quite simple and you can invite people to have fun in the group chat for project discussion purposes.
