Update from my side. I enabled the key again, and I now get a phone number verification step on login. It appears that I need to enable a Twilio SMS number in South Africa for me to be able to send SMS's via Twilio - I'm waiting for the paperwork to get completed for that. So it _appears_ to work at this stage, but I will only be able to fully test the functionality once I get the SMS-enabled number for Twilio.