> This is very good, because billing the EU is quite strict, and having someone get the format right for me is super useful :)

Is it? In my (EU) country there is basically a list of things the invoice must show, without any strict template, even if they converge on very similar designs in the end. Basically to allow branding and alleviate physical -> digital transition struggles.

In the beginning the most popular "invoicing" software was Excel :D