Normally the Tax Invoice sent to Attendees states that gst is included.However if all your projects in your account are non GST your account can be changed to a non gst account which means there is no reference to GST on the Tax Invoice. If you require this please submit a ticket to request your account be changed.
Note that a My Booking Manager account can be either gst or non gst. If you have some projects where gst applies and others that are non-gst, the only solution is to set up a two My Booking Manager accounts, one with gst, the other with no gst. (No setup fee applies for the second account).