Welcome to the Community forum,paula-tmsullivan.

You don't need to mark billable the bill.You can only tag your project in bill under the customer/project per line item on your bill transaction. Here's how:

1. In the left menu, click the + New button. 
2. Choose Bill.
3. Select the vendor's name in the Vendor field.
4. Under Category details or Item details, and find your bills, then choose a specific Customer/Project make sure that you fill out the project name under the customer column.
5. Tap Save and close. 

For more information about projects and managing bills, see the articles below:

• Enter and pay bills.
• Projects FAQs
• Set up and create projects in QuickBooks Online

I got you covered if there's anything else you need. Just reach out to me, and I'll make sure you're taken care of. Have a lovely day!