People think that money can buy everything for them and to an extent it is true also but there are some things which money can’t buy and happiness is one of them. It is a debatable topic whether money and happiness go hand in hand or not.
In the beginning if you are short of funds and once you start earning money then it can certainly lead to happiness because imagine a situation where you have $1000 dollar and you want to go to vacation but it costs $5000 then you would be sad because you missed happiness arising out of good time you would have spent if you were on a vacation. If you had $5000 then you would have been happy so you can say that when a person makes a transition from low income to high income group then there is a positive correlation between money and happiness which means the more money you earn the more happy you become because you start doing things which was not possible earlier due to lack of funds.
Now take the case of wealthy people who have millions of dollars, but still they are not happy. Their grief may be due to their strained relation with their relatives or due to some illness which is incurable, and many such factors. In real life one see many such examples where a person is wealthy still from inside he or she is not happy and no matter how much money they have, they remain unhappy. So in case of these kind of people one can say that there no correlation between money and happiness.
As one can see from above there is no set rule that if you have money you would be happy and if you do not have it then you would be unhappy. In reality there are many variables apart from money which decides whether you would be happy or not.