Hello dan303,

Thanks for posting in the Community!

Once the GST is turned on and set up in QuickBooks Online we're unable to turn it back off. You'll have to set your default tax rate to Out of scope in your company settings to not calculate GST on your transactions. Let me guide you on how:

1. Click on the Settings icon.
2. Click on Account & Settings, and click on the Advanced tab.
3. Under the Accounting section, set Default tax selection to Out of scope.
4. Click on Save and Done.

You can also check this link to learn more about How do I turn off GST?.

Post again in the Community if you have more questions. I'll be around to help you!