You can use a file stored in Dropbox to update the inventory quantity in your Shopify store via a shared link using EZ Inventory.

1. In Dropbox, select the file and click the "Copy link" button.

This will provide you with a view-only link to the file.

2. In EZ Inventory, create a Data Feed. Then under Source Data > Feed Type, select "Web (HTTP/HTTPS)". Set the Format option, and paste the link under "Website URL".

3. In the Field Mapping section, specify the column/field names.

4. (Optional) If you'd like to schedule the inventory update to run automatically, you can do so under the Schedule section.