Sales Invoice Template was a Settings category literally several hundred versions ago. It held only a very few parameters, such as the invoice title, prefix symbols, etc. Customized sales invoices have, for a long time, been under the View Templates category. That is what @davew is referring to.
Without resorting to HTML coding, however, you can add bank details in three ways:
- Enter them under
Settings=>Business Details, which places information in the upper right area of the invoice - Use custom fields, which places the information at the bottom. See this link.
- Place the information in the Notes field. You can set default text there which comes up on every new invoice (not old ones). Note that formatting in Notes is controlled by HTML coding, however. But you can do very simple things without knowing HTML.