A Hybrid Mobile App for Business With Inbuilt Chat

My business is looking at creating a mobile app for different roles of users. The backend chat system you need to suggest which one we can use that has ready made interfaces to work with the mobile apps. Different groups of users can be added. One group will be monitoring all incoming chats and adding more users - searchable by group name to the chat. Chats can be created, archived. Notifications for incoming chats personal and group level ( all whatsapp notifications required) Chat history is required to be seen and searchable on the mobile apps. Except admin no users will use the web systems and all groups will register via the mobile app and can be authorised by the admin to use the system. Please quote your best rates and if the costs are high we are open to increasing the bid. DO MENTION IF YOU HAVE DONE CHAT SYSTEMS BEFORE AND POST PORTFOLIO WITH PREVIOUS APPS DONE. YOU ARE FREE TO SUGGEST THE FRAMEWORK YOU WANT TO USE WITH JUSTIFICATION.