Thanks for getting back to us, @MelanieCharlesworth.

Let me provide additional information about your concern in QuickBooks.

At this time, we're unable to add an inventory to a project. You'll have to create an invoice for the inventory you wish to take and use to the project.

Also, you can use the advice of @vpcontroller provided above in creating invoices.

In case you need some related articles for your future tasks, you can always visit our Income and expenses hub for reference.

To know more the latest updates and features in QuickBooks Online, you can check our QuickBooks blog for future reference:

Please don't hesitate to comment below if you need further assistance. I'm just around to help. Take care.