"Why is there a payment for it? Genuinely curious, why not just sell as it being the first few lucky to get it"
a) because it might not work
b) because you might be in the control group which gets the placebo shot
c) because it takes quite a bit of your time (repeat appointments, some lengthy
d) to induce people to allow into their body something which, although it has passed animal modelling and there is no reason to think would be harmful, has a unknown side effect profile
It is however likely that they will be tested for COVID, both immediately on developing any symptoms and alsinperioducally during the trial. And some people might see that as a benefit