Amazon mws api, paytm api, and Flipkart api

I need to create an online app which allows mws key and secret to be added, once varified it will fetch all the inventory to local database, will do the same on the basis of sku on all portals like Flipkart and paytm, it will then keep an eye on orders and update the inventory if sold on all portals. Please only bid if you had already worked on these APIs need to work will all three portals for the time and can be added more portals later