How to get information about sales customer from Sale via API?v

I have successfully been able to fetch information about Projects and Sales via the SuperOffice API.

However, there are some fields my client would like me to fetch from the Sales tab, for example the customer/company of the given Sale.

What I am referring to is the field named "Firma" ("Company" in Norwegian). I did not find this info via a standard Sale API call towards this specific Sale.