I have contacted RKD team. Based on the latest Fundamentals data guide (RKD API WM Fundamentals Dataguide Dec 2020.xlsx - download by clicking "Coverages" button), Financial line items are available via summary financials. The team suggests you check that "Selling/General/Admin. Expenses, Total" (SSGA) data.
I strongly suggest you contact the RKD support team directly via https://my.refinitiv.com/ website if you have further questions regarding the RKD content and Service that match your requirement.