Hi there, tonyjen609.
I saw your first post, and my colleague GlinetteC provided you with the steps on how to process a sales receipt. You can follow that and make sure to select GST Free from the GST column. This will record the payment without GST.
For more information about GST, you can check this article: GST & BAS.
Please let a comment on this thread if you have any additional questions or concerns. Thank you.