I'm a Shopify Expert, working in this environment for 4+ years of vibrant and industrial experience. I can create Shopify App and also upload on Shopify marketplace as per yours requirement. 

I have full command on Shopify API, live data integration, pushing data into your stores, pushing data into third party APIs, saving in Database, filtering, indexing, writing into files, showing into custom designed Shopify public apps or Private Shopify apps.

• Shopify API authentication.
• Shopify Web-hooks Implementation to fetch live data in milli seconds.
• Shopify background jobs with Shopify API to run any business logic on back-end server.
• Shopify public apps with any custom logic for your customers.
• Oauth for public app authentications and access to stores data.
• Write cron-jobs in your Shopify App.
• Shopify back-end any custom needs.
• Fetch ( Orders, Products, Inventory, Variants , Collections, Customers, Fulfillment etc )