The short answer
A reasonably current laptop or tablet with a proper keyboard, an up-to-date browser, and enough data for daily lesson use. A phone works in an emergency but is not a workable device for a full school day.
Online schooling does not need an expensive setup, but it does need a workable one. This is what actually matters, roughly in order.
A keyboard
This matters more than processor speed. Written work, longer answers and anything involving typing are painful on a touchscreen, and the pain shows up as shorter answers rather than as a complaint. A cheap laptop or a tablet with a keyboard case beats a fast phone.
A current browser
Keep the browser updated. Most “the site is broken” reports turn out to be a browser several versions behind. If something misbehaves, try it in a different browser before assuming the platform is at fault — it narrows the problem down in thirty seconds.
Data and load-shedding
Two practical habits go a long way in South Africa: download what can be downloaded while the connection is good, and know in advance which parts of the day work offline. A charged device and printed work for a two-hour outage turns a lost morning into an ordinary one.
One learner, one profile
If two children share a device, give each their own user account or browser profile. Sharing one means two learners signed into the same platform account, which causes exactly the confusing problems you would expect.
When something breaks
Before asking for help, note: what you were trying to do, what happened instead, the exact wording of any error, and which browser and device. Those four things usually turn a two-day exchange into one reply.