The Shopify Private App connection method allows you to retrieve inventory from other Shopify store without the need of installing Stock Sync app on that store.
But the other Shopify store has to create a private app. Steps:
1. Navigate to Shopify Admin > Apps.
2. Click on Develop apps for your store.
3. Click on Create an app.
4. Once click on the create an app, it will pop up this. You need to enter App name and App developer email. Then, just click on Create app.
5. Then, it will direct to this page. You need to select the tab API credentials to get the API key and Password.
6. To access the tokens you should click on the Configure Admin API scopes.
7. It will direct to this page, you need to find for Products and check the box of read_products. Once selected, click Save and Install app.
8. After installed the app, you can see the token, API key and secret key.
Shopify API password starts with shpat_
If you need to get inventory from Store A to Store B, please create the private app on Store A. And install Stock Sync on Store B.
Paste the API key and Password in respective fields and also the Shopify domain, storeA.myshopify.com gets from the Store A