How to add my ABN number instead of ‘Govt. UID’ to Tax Invoice?

Thank you for dropping by here in the Community, @cnomail.

In QuickBooks Online, you can configure the invoice templates and make changes to the information you want to show when creating the transaction. I suggest making sure you enable the ABN box from the sales form.

Here's how:

1. Click the Gear icon at the top, select Custom Form Styles. 
2. Choose the invoice template and hit Edit under the Action column. 
3. Go to the Content tab and click on the Header.
4. Make sure the ABN box is checked with the correct number.
5. In the Display section, check the custom field box which contains other ABN number if needed. 
6. Select Done. 

For additional information about how to customise invoices, check out the following article. It also contains detailed steps of the step by step process:

Customise invoices, quotes and sales receipts in QuickBooks Online.

I want to make sure this is taken care of for you. If you have any other concerns, post a comment below. I’ll pop right back in to assist further. Have a good one.