Price discrepancies exist between trading platforms, clearing firms, banks, etc if only for a small period of time. Options pricing is also affected for the same reasons but since there are other components involved in pricing an option than just the price of underlying currency, they tend to exist for longer periods of time.

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It seems that there is a long way to go to get used to professional trading platform from a retail platform.

In Currenex FIX protocol, a BUY limit order of EURUSD with base currency USD should be actually specified as a SELL LIMIT order.