The SLOW lounge is on the domestic side, which is separate from the international side (there are separate security clearance channels into the respective sides).

The airport website lists only the uMp(h)afa Lounge for the international side. It is described as "The uMp(h)afa lounge is open to all International passengers travelling out of King Shaka International Airport. A charge is levied per use thereof." I wonder whether that is that the lounge used by the handful of airlines operating existing international flights.