After Harry defeated the bad guys he decided to go to America. He settled in the New York area on a back street in an industrial area and converted the building he bought into security apartments.
The bottom floor he made into a cafe and grill kind of place with a bakery in back. Draco Malfoy came by and asked for a job so Harry hired him for the bakery, which he seemed to be really good at.
Other people began drifting in for meals when they smelled the food odors. One such customer worked at the local treasury mint where money was printed and shipped out to banks.
Harry was curious about how it all worked so he read the man's mind then obliviated him to have no memory his mind had been read.
So he it those memories in a pensieve to share with Draco. So z Harry's cafe was open from 6am to 3pm only unless they hired any other wizards
Harry investigated and discovered a billion dollars a year went thru the place in old worn out money that would be shredded. Harry's lunchbox he took to the mint was expandable with multiple compartments.
So here is Harry Potter wealthy wizard bored in America working at the mint trying to figure out how to steal 500 million in worn out bills, because he can use REPARO on them and they are restored good as new.
He can also take foreign currency and transfigure it e mass to look like worn out American money and just use a switching spell to trans the fake money for the real money that will become new money.
So Harry is switching out 100,000 dollars each day with fake for real money, realizing he will only be stealing 36 million per year. So Draco gets involved to help him a bit and now the two of them are taking 1 million per shift or 2 million per day, though they do have to slow down when the foreign banks get low on cash because they buy so much of it to trade the foreign ( fake ) money to switch out either real American money.
Inside of a year they have switched out 729 million dollars and hidden it in shrunken trunks. They send a shrunken trunk to Hermione Granger with 100 million American dollars and wish her a happy birthday and hope she enjoys her vacations in the south of France with her parents.
So one day Professors Sinastra and Sprout each get a shrunken package with 10 million dollars each from Harry & Draco.
Harry and Draco then begin to send roughly 250 million out of the country to all their former friends at Hogwarts.
Colin Creevy is checking the money when he notices the money looks awfully clean and hardly used for such old dates on it. Sh he goes to the goblin bank and ask them what with the money. He is told someone has used a very strong reparo charm on the money to restore it to new condition.
The money is good insofar as they can tell. So Colin goes to America to visit Harry and Draco, but discovers the bakery isn't open until 6 am and the cafe closes at 3pm.
He stops over at MAC-USA headquarters to ask about Harry and Draco, but they have not even seen them.
The very next day MACUSA drops by to visit Harry & Draco and see that the building has muggles in it so there can be no magical stuff around though they do detect some magic in use, but it is minor.
Harry & Draco are surprised that MACUSA visited them because Colin Creevy visited them and the Goblin banks the one in London and the one in New York City.
After MACUSA leaves they pull the folder on the money sent to Colin and it disentegrated into dust so he has no 'funny' money to ask about.
The goblins in New York though managed to remove the REPARO charm and the money regressed to it original worn out condition. They had one of their wizards who worked for them and the MACFBI to drop by the mint.
Bill Weasley was the worker and he came by after hours. Guess who he saw use a switching spell on money. He saw Harry Potter use a switching spell and not 4 hours later he saw Draco Malfoy use a transfiguration spell then a switching spell and then a REPARO on his shrunken trunk.
Bill teleports directly to their Bakery & Cafe business to ask them what they think they are doing.
Harry tells him he has checked the law and what they are specifically doing is not a crime. They get the same amount of paper by weight in foreign bills, then transfigure it from foreign money to real money, then switch out the fake money for the real money and then repair the real bills to look like new. This way the same amount of bills are shredded each day or evening. They take the newly repaired old money home with them and then it out to the former Hogwarts students who can take it to any London bank and exchange it for British pounds.