The UK government's information is not relevant. This is a matter for the South Africans. IATA's TIMATIC database is available through a number of free channels and you would be best advised to complete the database form with your exact details and, presuming that your passport and passport pages are correct, keep a hard copy printout with you. It is what the check in agent will see on his screen, but it's helpful to have the entries to double check.

https://www.united.com/web/en-US/app...aspx?i=TIMATIC