Welcome message Viber, FB Messenger

Hello,

I would like to ask about how to send a welcome message for users coming for the first time for channels Viber and FB messenger.

Viber - https://developers.viber.com/docs/api/rest-bot-api/#sending-a-welcome-message
FB messenger - https://developers.facebook.com/docs/messenger-platform/reference/messenger-profile-api/greeting/

Where can we set the text which would be used for first time greeting for both of these channels?

Thank you!

Its not yet scheduled for development but we will consider it as the product backlog item.