The complaints have a point.
If you use a FeaturePhone & not a SmartPhone then you *can't* use an app to register for, schedule to get, nor to validate that you have received your vaccination. In a country where 2G, 3G, & 4G are their network backbone for cellular & less than 60% of their population can even use that to get online, how exactly do you propose the poor folks obey your demands to do what is technologicly impossible?
"We made it a law that everyone drives on the right side of the road from now on." Umm, that's nice, but I don't own a car. Can't afford one. Not that it matters, the nearest petrol station to my home is over 100KM away. "That's beside the point! You are required to drive as we've made law!" Ok, you have fun with that. I'll walk on whatever side of the street I damn well feel like, kthanxbai.
If you only have a 2G FeaturePhone & can only use it when you've got the spare cash to buy a ~10minute PAYG card, even if you COULD use the app, you couldn't afford the data rates it would burn through like a pirahna through a bleeding cow. =-(