Many thanks Andrei for your prompt reply. The 'display tax suffix' was already checked.
I will explain in more detail for you. My New Zealand GST (Goods & Services Tax) number is 40-860-401. In order for customers to claim this tax content back, I must display this number on each invoice.
There may be a field that I can somehow add this line in (ie GST: 40-860-401) to keep the taxman happy!
Can this be changed directly on site by the end user with no fuss (with a text editor), or do I need to get in a developer to "recompile" the whole project and upload a new "build"?