Hi @tuba, and welcome to the SeaTable community!
That’s a pity that you didn’t receive much answer: it looks amazing! Maybe @webdienste may be interested, I remembered he actually posted a thread and a feature request on this subject.
I don’t know if you plan to extend your application to other languages/countries, but electronic invoicing seems to have been (or is in the process of being) implemented for various EU countries.
Unfortunately, in France, electronic invoices must be transmitted via an approved platform 
.
Bests,
Benjamin
