Well, we don't know what weight you're starting from. We don't know anything about you. If you're a lot overweight, sure, that's not that much to lose in a month. If you're not overweight, of course that would leave you malnourished. And that's not enough calories for your health. Why do you have to lose weight quickly, and why are you considering such a starvation diet to do it? How much do you exercise? Etc.
A 499 budget of calories a day is not realistic. Are you saying that is all that an app is saying you should eat to lose this weight? That's not possible. Or healthy. Remember, the faster you lose weight, the sooner it returns. Try to have a more long range goal that allows you to eat a normal amount for the day which is not under 500 calories hon. good luck
Maybe you can try the military diet? I havent tried it myself, but it seems very effective. Surviving with only 499 calories a day for a month is in my opinion unhealthy and maybe kind of impossible if you want your body to work properly. Maybe you can go see a dietist?