does viber api allows you any way to send branded messages throw your application and get answers without partners mentioned on this page https://info.viber.com/Viber-Business-Messages-Partners.html ? Or maybe is it possible to make your bot administrator of community and send notifycations such way? I made bot but it could only respond on users requests also got viber buisness acc.
If you have Viber bot already - then you are able to send messages when you need to notify them, not only during processing incoming request.
Everything you need is to remember chat_id somewhere (file or DB), initialize bot entity at desired moment (as you do that during request handling) and call send_message (with chat_id and message that you want to send.