An order rejection occurs when a trading server declines to execute an order instead of filling it. Common reasons include the quoted price no longer being available, insufficient free margin, a volume outside the instrument's permitted limits, a maximum deviation setting that the new price exceeds, or a liquidity provider declining the trade during a last look window.
The platform normally returns a rejection code or message explaining the cause. Rejections cluster around economic releases and thin periods, when quotes change faster than orders can reach the server. Frequent unexplained rejections are one of the things traders review when assessing execution quality, alongside fill ratio and slippage statistics.
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