Stock Sync is a 3rd party application that can be added to a Shopify store. For the most success, we recommend installing this for a nominal fee. Stock Sync will sync up your store inventory with Global Crafts to prevent oversells. In addition, it offers a way to add and update products for the Global Crafts catalog.
Stock Sync Support:
Info to get started on Shopify store to store (add/update):
https://help.stock-sync.com/article/94-shopify-store-to-store