Hi,
I am a PhD of artificial intelligence. I have 18 years experience in software development.
I can design an ML based chatbot for u.
I propose you 4 options for the backend:
1- PHP+ AngularJS,
2- ASP.NET MCV Core.
3- Node.js
4- Python+ Flask
I can also develop app in both iOS and android with the best quality.
We can negotiate more on chat.