Two abn numbers on invoice and first is incorrect

Hello there, @coolummowing. Welcome to QuickBooks Community!

I'd like to share some information about changing an ABN number within your QuickBooks Online (QBO) account.

You only have one ABN number recorded in QuickBooks. If you want to correct your ABN number, you can follow these steps.

1. Go to the Gear icon.
2. Select Account and Settings under Your Company.
3. In the Company tab, select the Company name section. From there, you can change the ABN.
4. Click Save. Then, Done to reflect the changes.

That should work. Since you're seeing two ABN numbers, it could be the other one is your client's ABN number. This happened when the Customer ABN number is ticked in the invoice template. Here's how you can verify it:

1. Go to the Gear icon. 
2. Select Custom form styles.
3. Select the template you're using. In the Content tab, review the ABN field and Customer ABN field. (If you don't want to include your customer ABN number, you can uncheck the field).
4. Then, Done.
   

See the sample screenshot below. The first one is the ABN number of your customer.

You can use these resources to manage your business and contact information. The other resource is where you can learn more about customising your sales forms.

• Learn how to update your business info in QuickBooks Online.
• Learn how to personalise and add specific info to your sales forms.

Please let  me know if you have more concerns. I'm always around to help you further. Stay safe and be well, coolummowing.