To track and sync your inventory in QuickBooks Online using Pipemonk, you will need to create an Inventory Account.
Here are the steps to create an Inventory Account in QuickBooks Online:
1)Click on the Settings (the gear icon) in your QuickBooks Online account:
2)Click on 'Chart of Accounts' in the 'Settings' column:
3)In the Chart of Accounts page, click on 'New': 
4)Choose the ‘Category Type’ as 'Other Current Assets': 
5)Choose ‘Inventory’ from the Detail Type drop down menu: 
6)Give an appropriate ‘Name’ to the account. By default it is same as the “Detail Type” you choose: 
Click ‘Save’. Thats it!
An Inventory Account has been successfully created in your QuickBooks Online. When you reload Pipemonk Sync Settings, this Inventory Account can be used.