Yes right.
> The 48-year-old, who can neither read nor write, would need to call his son to confirm that the payment had been received.
Looks like the author made up a narrative. These vendors definitely can read numbers, they manage loads of cash through the day. They do lightening fast calculation in their head - which would put a Math grad student to shame.
They may not be able to read, write English (or other languages) but they are very comfortable with numbers and operations on them (addition, subtractions...).
And they would not need "their son" to confirm the amount (they can read), and also they would recognize a very large green checkmark (an icon to confirm successful transaction), so don't need "their son" for that too.