Could you please explain how currency exchange works? Why is there such a large price discrepancy? Shouldn't the buy and sell prices be approximately equivalent? And how do I sell a Spirit Gem for 190ex?

Quick tip: just hover over the price ratio and press Alt and you can see both buy and sell orders at the same time 👍

It's not really related to the currency exchange per se, it's common in many systems IRL too. if you want to understand more you can search "Bid-Ask spread"

it works like an order book. there are orders for sale and purchase.

Its what people are buying for and what people are selling at. Just list it lower then 190 and someone will have to pay ur price if they want to buy it then and now.

That’s one way to make currency if you are on low budget.. find those “gaps” and use them.. it’s not illegal

So can someone explain it like I'm 5? How do I see the currency that is being sold under value?

The gap is so big because the league is dead and people aren't buying enough

When there's few people playing, price spreads are commonplace. You can arbitrage the spread but it has a high gold cost and ties up your limited 10 exchange slots.

That’s called the spread, usually a spread this large means that this item is not very liquid. I.e not frequently traded.

You can’t sell it for 190 exalts. 37ex is what people are willing to buy it for. 190ex is what people are willing to sell it for.

Because you might be willing buy something for less than what people are willing to sell it. But most times is people trying to buy cheap sell expensive.