Using the Viber API and especially the "broadcast" feature (https://developers.viber.com/docs/api/rest-bot-api/#broadcast-message) all the rich messages on Android are sent and shown normally, although in all iphones that I have tested, the image of the rich message is not showing at all.
Using Python
url = 'https://chatapi.viber.com/pa/broadcast_message'
headers = {
'X-Viber-Auth-Token': viber_token
}
data = json.dumps(_broadcast_template, indent=4)
broadcast_response = requests.post(url, headers=headers, data=data)