While Pope Leo X certainly had his many faults,
"SELLING of indulgences" was NOT one of them.
What the Pope authorized was the Preaching of an Indulgence all across Europe,
with all the usual attached conditions (genuine repentance, contrition, prayer for the Church and the intentions of the successor of Peter, rejection of attachment to sin),
for those who would make a charitable donation of any amount, for the rebuilding
of the decrepit St. Peter's Basilica.
He was not "selling" the indulgence and, contrary to the wickedest lie ever
told about this, he was definitely NOT "selling salvation", as a Presbyterian friend
once nastily characterized it.
There were, however, some unscrupulous preachers, at least I have heard, who
did make remarks similar to "As soon as a coin in the coffer rings, a Soul
from Purgatory SPRINGS!!"---- although even that is Martin Luther's sarcastic caricature
of what some of those men said, and Luther was well known for his extreme sarcasm.
But the Holy Father never, NEVER, "sold" the indulgence.
You can't just give a certain amount of money and actually receive an indulgence.
It doesn't, and has NEVER, worked that way.
God bless you,