Viber Service Messages can only be sent by businesses that have been approved by Viber. This business profile will also have a green check to indicate that it is a legitimate business.
The advantage of Viber Service Messages is that the identifier of users on the platform is their mobile phone number. The business accounts are limited to only outbound messages to the customer. This means there is no way for a customer to respond and means that you don't need to worry about dealing with inbound messages.
In order to get started with Viber Service Messages you will need to email email@example.com. Nexmo is an official partner and will handle the application and creation of your Viber Service Messages account for you.
If successful, your account manager will provide you with a Viber Service Messages ID. This ID can only be used on Nexmo.