To include the ABN on your invoice, we'll need to customize your invoice template in the Custom form style, Natasha. Allow me to help you further.

Here's how:

1. Go to the Gear icon.
2. Select Custom Form Styles.
3. Choose Edit on the Default invoice, or create a new template by clicking the New Style dropdown and hit Invoice.
4. Navigate to the Content tab, then click the top box within the invoice preview.
5. In the Header section, ensure the ABN checkbox is marked as checked.
   
   
    
6. Click Done to save your changes.

Feel free to drop a post below if you still need further assistance.