Build me an Android app for deals with chatting functionality

Brief description 1. We need an application for Android with a possible backend (restaurant and main admin end) which is common for all three platforms- web, android and ios. 2. We want to develop a coupon/discount application for restaurants and cafes and a system through which we can sell Knocksense membership to end users. 3. We want to have a restaurant/cafe manager backend through which they can manage their offers and also check the details of people who have unlocked their discount coupon/deal through our application. The backend system will also support a chatting functionality with the frontend users. The chatting option will have preset messages and option to ask preferred discount value associated with a product, which will be selected from the menu of the cafe/restaurant. 4. This chatting will also enable users to reserve table at the cafe/restaurant. The cafe owner can either accept or reject. I will share all the preset messages and instant replies with the developer. These preset messages will have blanks which will be filled by the user on both the ends. 5. As an admin, we also want to keep a check on the bookings, chat messages and accept or reject discount/coupons on store vendors behalf. We will need to integrate a payment gateway which is popular in India, through which people will be able to purchase Knocksense membership. The payment gateway must also provide the invoicing functionality, thus we recommend using Razorpay. 6. The app will also have to integrate certain sections of our website eg all blogging pages. We are currently running a content website on Quintype. API- a. [login to view URL] b. [login to view URL] 7. We need push notification features for the following cases- a. Subscribe to Knocksense platinum b. Subscription renewal reminder c. New messages d. Option to send push notification for hot offers or any offer e. Reminder for coupon expiry 8. We will also need integration with SMS and newsletter services to send reminders to our users. 9. The app must be smooth and fast. We would like to keep on adding new features in the app such as full-fledged table reservation and Delivery functionalities later on thus the app must be future-proof on all ends, which includes Security features and user data protection.