making a new invoice

[Mw. Mr. V.M.H. Schaars]

Dear all,

The invoice included in gnucash is not sufficient for me. So I want to
create my own. Before I start, I want to know: Are there any invoices
available already? 

Also, copying and renaming the file register.scm and adding it to the
list in report-list.scm resulted in an error when trying to start
gnucash:
ERROR: In procedure scm-error in expression (scm-error (quote
misc-error) *f ...): 
ERROR: no such module (gnucash report invoice)
What else do I need to do to make my new report visible in gnucash so I
can test results?

Kind regards,
Veronique Kwaaitaal