Hello scott-insightacc,
Welcome to the Community!
QuickBooks Online only allows you to lodge your BAS in chronological order. You'll have to request to unlodge/reversed December 2021 BAS period to be able to lodge your September 2021 BAS in QuickBooks Online. Or if you have an accountant that uses QuickBooks Online for Accountant, you can add them as an accountant and they'll be able to unlodge the BAS period.
Our Customer Care Team can help you unlodged the specific BAS period in a secure form, please contact support through this link https://help.quickbooks.intuit.com/en_AU/contact
To learn more about how to prepare your BAS in QuickBooks Online, you can check this article How to lodge a BAS or IAS in QuickBooks Online.
Feel free to message us back if you need any help with your BAS. Have a nice day!
