How does the currency exchange service work?

Question

ASP.NET

Hello, I want to make a currency exchange service on Asp net.
The question arose, how to implement the exchange?
I presented 2 options:
1) Use the api of some exchange, accept currency for exchanging the exchange’s wallet, make an exchange when money arrives and withdraw to the specified wallet.
Of the minuses here is that I cannot guarantee the exchange rate, that is, the person clicked on the exchange button, and the exchange itself will take place later (until the money arrives, etc.)
2) Create wallets with currencies, fill them with some kind of balance and everything to do it is to receive on the balance of one wallet and give from another.
Of the minuses, you need a large supply of money.
Are there any other options? Naturally cheaper than the first option.

Answer 1

Second? Cheaper than the first?
It's funny
, but what then is the gain, if in the first case the exchange is 1k1 at the exchange rate? Is that if you sell a smaller number of received currency. But it's not serious at all.
All exchangers are now working on the second way, but this is very, very rude