Hi pmoon, 

There are a few things that could impact this. First, it's important to check if you have turned on GST in the company that you are working on - if it has not been enabled, then you won't be able to set a tax code and all transactions will not include GST by default. To check this, first go to the GST tab on the left of your page - if it is asking you to Get Started, then you will need to click on the green button and enable a frequency for BAS, even if you aren't going to be recording any BAS figures. Once you have saved these settings, GST will be enabled and you will be able to record tax codes on transactions. If you are not registered for GST, though, then you don't need to go through these steps to enable GST tracking, as you don't need to record it in your company. 

If you have any further questions about this, you're welcome to reply in this thread, or if you'd rather speak to a member of our support team directly you can give them a call on 1800 046 038 and they'll be able to go into some more detail for you. 

-Lucas