When implementing an Inventory class for checkout and indicating that inventory is available for all items and amounts in the cart, the correct step is to return sfdc_checkout.InventoryStatus.Status.SUCCESS. This indicates to the checkout process that the inventory check has passed and the items are available. Salesforce documentation on customizing inventory validation in the checkout process would detail the expected return types and values, ensuring that developers implement the inventory checks in a manner consistent with the platform's requirements.