Yep, it is only to get through JNB Customs/Passport security and yes it is a waste of time and money.
I went round and round with a SA Airlink ticket monger to get on a flight to Bulawayo as they wanted a 48 hour or less PCR test - which is impossible to do if you're flying in from the States. So a quick PDF edit and problem solved.
Asshats...
