I am looking for a documented process on the following.
We have a retailer and supplier who uses Shopify to sell their products. We have signed up as a dealer with them and we use Shopify too. How do we properly manually create an app on the store to connect both websites so that when the supplier updates their inventory levels it will reflect back into my store as well? We currently created an API through the shopify store and created a manual app to connect both stores but I am looking for a documented process for this.
Products have Product Variants, Variants have Inventory Items, and Inventory Items are tied to Inventory Levels which represent an Inventory Item that can be fulfilled from 1 or more locations they have. The Inventory Levels are what you'll want. Depending on your choice of REST vs GraphQL, you may need to make use of API pagination for the REST version, or the bulk query feature for the GraphQL version.
You could also look into discussing best practices with a Shopify Expert.