They were one and the same until some people protested against the Catholic church telling people they could buy their way into Heaven - https://en.wikipedia.org/wiki/Ninety-five_Theses
The sale of indulgences was a charitable donation done to mitigate the penalties of Purgatory.
Abuses were committed, but the telling of the protestants is quite fantastic. It was not, for example, a get-of-Hell sale