I have several purchase orders with the same client, which i need to reference on an invoice. Is there a field so I can track how much has been billed against each?

Thanks for your time today, @alex41,

I can share some information on how to track how much you bill your customers in QuickBooks Online.

When you bill a customer, you can assign a memo on the Message on invoice section of the invoice. This way, when you run a customer report, you can track which transactions are billable. Check out this snapshot:

Once you assign the memo, you can customise a Sales by Customer Detail report to view billable sales transactions. Here's how:

1. Go to the Reports menu.
2. Select Sales by Customer Detail.
3. Click the Customise button.
4. In the Rows/Columns section, click the Change columns link.
5. Mark the Client/Supplier Message box.
6. Hit Run report.

Here's how the report looks like:

That should do it. Please let me know if you have other questions. I'll be around to help whenever you need a hand. Have a nice day!