Setting invoice template from Billable time

How do I set the invoice that is issued when I create invoice from Billable time that has customised messages? I’m having trouble getting the invoice template set up to automatically include messages about payment, invoice dispute process and professional liability. I’m required by my professional body to include these statements and I can’t seem to make it work. Thank you

set them as defaults for your sales invoice under Form Defaults.

You will probably need to create custom fields first.