Passport required to book apartment in South Africa

I just booked through booking.com a flat in Cape town for february.
The owner sent a mail asking for passport copy saying authorities require it.
It really looks weird to me as they can get my copy at check in as everywhere else.
Do you know if it's a normal request i South Africa?
Thanks

It looks like ID for hotels is a requirement in South Africa:

https://www.pembba.co.za/page/guest_identification_requirements

But it doesn't appear to be a requirement for them to take it beforehand.