Upgrade Android Pure Java application - E-Voucher

My project is to update an exist Android Java project. The solution is an E-voucher system which is a software that provide POS solution that work offline on mobiles phone. The main purpose is managing voucher and it’s balance, managing Vendors and their products using NFC cards. Now I need to update the mobile app, here are the description for the updates needed for our application: Core system: • Downgrade the app to work on android 4 or higher, Now working on Android 5. • Change printer SDK to our new device • Disable on NFC card tap open new invoice 1- Login: 1. Vendor login with NFC card instead of username and password. 2. Allow multiple vendor to log into the same device 2-Invoices: 1. Dynamic price with validation between min and max (min=max => static price). 2. Pin code on paying an invoice. (this pin could be Number-Colors-Photos) 3. Balance Expire (Balance could expired on specific date) multiple top-up for the same card each one will end in different date. 4. Enable / disable pin code, signature, photo according to value from DB 3-Vendor Function: 1. Payment from vendor side. a. payment request (Select invoices to be request to paid- save this information not be paid again) b. Payment receiving confirmation (after accepting from admin portal) 2. print report with start end date with add button for (day, week, month) 4-Field Officer 1. setup card pin in three types (Number-Colors-Photos) 2. Benef. signature on setting up pin code 3. update balance when setup pin 5- Show card information 6-Design: 1. Home page shows: a. Products b. Reports c. Sync d. Payment 1. Enhance choose product mechanism 2. When click on product allow vendor to add the quantity of product and the price 3. Deploy design as provided from designer (Colors, Icons) 7-Roles: (all these functions depend on variable from the web) 1. Role for report 2. Role for create/show invoice 3. Role for create/show payment 4. Role for setup card pin 5. Role for Card information 8-Backup on SD card 9- Doing all API changing need on the web server. The application now is working, those are just update. More explanation could provided