If inventory needs to be pulled from a specific location, the location can be looked up from the URL directly, as shown in the screenshot below. Just ensure that Onport has access to "Inventory".
Important! The inventory location must be the correct numeric value otherwise inventory quantities will not sync.
After retrieving the Shopify location Id you can place it in Onport under Inventory > Inventory Feed > Settings > Connections Tab > "Inventory Location ID"