You can set up the ABN number as an additional field onto your organization profile. To do this:

• Click the Settings tab.
• Under Organization Settings, click the Organization Profile link.
• Scroll down to Additional Fields, enter "ABN Number" in the Field Name and update the actual ABN number in the Value column.
• Once this is done, click the Save button.

Now, all you need to do is include the Additional Field Placeholders on your Invoice Template. If you are using custom templates for your invoices, make sure to add the placeholders %CompanyCFLabel1%:%CompanyCFValue1%, to your template. Please follow the below steps inorder to include Additional Field Placeholders.

• Click the Settings tab and under Preferences, click Invoice Templates.
• Edit or Customize the Invoice Template that is used.
• Select "Organization Details" in the first drop down menu next to Placeholders.
• Select "Label 1" below "Additional Fields" in the second drop down menu.
• Copy the generated text (%CompanyCFLabel1%) from the third drop down menu and have it pasted below your organization details.
• Select "Value 1" from the second drop down menu and have the generated text copied and pasted next to "%CompanyCFLabel1%".
• Once this is done, click Save.
• Note: Follow the same steps to include VAT number as well. In the Field Name simply mention "VAT ID" and enter the actual VAT number.
• For more information on customizing invoice templates, please check the video tutorial: Customizing templates in Zoho Invoice