From FIXwiki

FIX Message OrderCancelRequest (MsgType=F)

MsgType	FIX Specification	First introduced	Deprecated
MsgType=F	Trade messages - SingleGeneralOrderHandling	FIX.2.7

The order cancel request message requests the cancelation of all of the remaining quantity of an existing order. Note that the Order Cancel/Replace Request should be used to partially cancel (reduce) an order).

The request will only be accepted if the order can successfully be pulled back from the exchange floor without executing.

A cancel request is assigned a ClOrdID and is treated as a separate entity. If rejected, the ClOrdID of the cancel request will be sent in the Cancel Reject message, as well as the ClOrdID of the actual order in the OrigClOrdID field. The ClOrdID assigned to the cancel request must be unique amongst the ClOrdID assigned to regular orders and replacement orders.

An immediate response to this message is required. It is recommended that an ExecutionRpt with ExecType=Pending Cancel be sent unless the Order Cancel Request can be immediately accepted (ExecutionRpt with ExecType=Canceled) or rejected (Order Cancel Reject message).

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Notes

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For example if you were writing a clarification on how to specify the "quantity" of an order in FIX, you might add the
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