How does IOI make money accepting Oasis currency?

"Coin"/Credit is a stable currency in OASIS...but it seems valued outside of the OASIS.

The IOI doesn't necessarily have to make a profit on these things, after all, they don't really exist so it gives the players something to aim for while using IOI's services...since they are the leading internet provider.

Innovative Online Industries. IOI (pronounced eye-oh-eye) was a global communications conglomerate and the world’s largest Internet service provider. A large portion of IOI’s business centered around providing access to the OASIS and on selling goods and services inside it.

Items in the OASIS had just as much value as things in the real world (sometimes more), and you couldn’t pay for them with food vouchers. The OASIS credit was the coin of the realm, and in these dark times, it was also one of the world’s most stable currencies, valued higher than the dollar, pound, euro, or yen.

Over the past five years, I’d managed to slowly, gradually raise my avatar up to third level. This hadn’t been easy. I’d done it by hitching rides off-world with other students (mostly Aech) who happened to be headed to a planet where my wuss avatar could survive. I’d have them drop me near a newbie-level gaming zone and spend the rest of the night or weekend slaying orcs, kobolds, or some other piddly class of monster that was too weak to kill me. For each NPC my avatar defeated, I would earn a few meager experience points and, usually, a handful of copper or silver coins dropped by my slain foes. These coins were instantly converted to credits, which I used to pay the teleportation fare back to Ludus, often just before the final school bell rang. Sometimes, but not often, one of the NPCs I killed would drop an item. That was how I’d obtained my avatar’s sword, shield, and armor

^{Ready Player One - Ernest Cline}