From FIXwiki

FIX Message CrossOrderCancelRequest (MsgType=u)

MsgType	FIX Specification	First introduced	Deprecated
MsgType=u	Trade messages - CrossOrders	FIX.4.3

Used to fully cancel the remaining open quantity of a cross order.

Message Contents By FIX Version

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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