I will also add an opinion from the integrator:
1) it seems that the principle of separating the personal messenger and the bot (in which the clients have to write first) will remain the basis for all chat systems for the purpose of basic spam control
2) for Viber - who exactly knows the difference between a bot and business chats? I haven’t found one yet and I assume that the functionality is the same, only paid, with the ability to write first and without the ability to write back to the client (advertising message)
https://www.forbusiness.viber.com/3) we have successfully set up the following process for our clients through Box without modifications:
a) Turbosms bought a paid viber called Mobibon for themselves, which they allow everyone to use as a transit account for sending paid viber messages individually
https://turbosms.ua/ua/news/viber-rassilka.html the price is now from 36 kopecks to 1, 45 hryvnias The main condition is to send not spam, but work messages, as long as Turbosms itself has not banned you (because of course there is a risk that they will be banned for this, but it still works)
b) from the Box, we send a message with the action "Send a universal Viber/SMS Turbosms message", in which we embed a button to go to our Viber Bot, where the client can write back and continue the full correspondence here. You can embed the order ID in the link and then the client will be automatically attached.