Hi there, @jaidev.
Welcome to the Community. QuickBooks Online Essentials will only let you track non-inventory, service, and bundle.
Hence, the feature to add the cost of an item is only available in the inventory item which is applicable in the Plus and Advanced version of QuickBooks Online.
You may want to consider upgrading your subscription to the higher version of QuickBook (Plus, Advanced) so you can start using this feature. Here's how:
- Click the Settings (gear icon), then select Accounts and Settings.
- Go to Billing & Subscription at the left pane.
- In the QuickBooks Online section, select Upgrade.
- Choose the plan you want, and select Upgrade.
- Confirm your payment information, then select Save.
You can also visit our plan and pricing page to see the lists of plans and features that best suit your business needs.
For future reference about adding products and services in QuickBooks Online, check out this link: Track inventory in QuickBooks. This feature lets you add your inventory products so you'll know the quantity on hand of your inventory items.
Feel free to message again if you need more assistance. We're always delighted to help.