Welcome to the Community, Skillcraftoffice. You can add another expense to your bill/invoice.

To do so, you follow the steps below:

1. Go to Myapps and then Projects.
2. Navigate to the Transaction tab and locate the bill.
3. Under the Action column, click View/Edit.

1. Add the missing expense, check the Billable box, and assign the Customer/Project.
2. Click Mark as paid and Save as New.

However, this action will increase your accounts payable balance with your vendors. Afterward, ensure to check the box for billable, then select a customer/project. Once the bill is paid, you can mark it as settled.

If you have any additional questions about adding a bill to invoices, please don't hesitate to reply to this post.