I'm not talking about the law of one price here, just the fact that the global currency exchange trade is decentralised. There's no one exchange that aggregates everything and can give you a single authoritative price.

In other assets, like equities, there often is a single central exchange. If you want to buy CURI for example, it's only listed on NASDAQ, so the price on NASDAQ is The One True Price as far as a normal person is concerned.

There's no such central exchange for currencies.