Where can I add a California contractors license number so it shows on the header of my estimates/invoices etc?

Hi there, chad. 

In QuickBooks Online (QBO), we can customize our sales transactions using the Custom fields functionality. However, this is only available in Essential, Plus, and Advanced. 

To create a Custom field, we can: 

1. Go to the Gear icon. 
2. Under the Lists column, choose Custom fields. 
3. Click the Add field button. 
4. Enter its name. 
5. Tick the All Sales forms. 
6. Toggle the Print on form to appear on the printed versions.
7. Click Save. 

Furthermore, browse these articles to learn more about managing your sales forms in QBO: 

• Customize invoices, estimates, and sales receipts in QuickBooks Online
• Record invoice payments in QuickBooks Online
• Convert an estimate into an invoice in QuickBooks Online

If you have additional questions about invoices and estimates, hit the Reply button. Keep safe!