Here is my question. Considering the critical nature of the errors I discovered, I feel I deserve some form of a reward. Reasonably speaking, what kind of reward do you think I could ask for?
I doubt error/bug you found could be categorized as critical. Most of critical vulnerability i know is about enabling hacker take control over your computer or steal your data (if it's encrypted). Even so, if it's subscription-based app/service, i would ask for few months (between 6-24 months) of free subscription.