Looks nice.

Consider making it possible to test the tool without signing up.

Is this for use in the US? Have you looked into electronic invoicing formats which are increasingly used/required in the EU ... I am curious if there is a similar move on the way in the US.

(As an example here is what the electronic invoicing format looks like in Denmark: https://www.oioubl.info/downloads/OIOUBL_Bekendtgørelse.pdf (scroll a bit past the Danish mumble to see the structure of the XML-documents interchanged.))