From FIXwiki

Message Content of PositionReport (MsgType=AP)

TagText	FieldName or ComponentName	Required	Description
	StandardHeader	x	MsgType = AP
	ApplicationSequenceControl
721	PosMaintRptID	x	Unique identifier for this position report
710	PosReqID		Unique identifier for the Request for Positions associated with this report This field should not be provided if the report was sent unsolicited.
724	PosReqType
263	SubscriptionRequestType		Used to subscribe / unsubscribe for trade capture reports If the field is absent, the value 0 will be the default
727	TotalNumPosReports		Total number of Position Reports being returned
728	PosReqResult		Result of a Request for Position
325	UnsolicitedIndicator		Set to 'Y' if message is sent as a result of a subscription request or out of band configuration as opposed to a Position Request.
715	ClearingBusinessDate	x	The Clearing Business Date referred to by this maintenance request
716	SettlSessID
717	SettlSessSubID
423	PriceType
120	SettlCurrency
1011	MessageEventSource		Used to identify the event or source which gave rise to a message
	Parties	x	Position Account
1	Account		Account may also be specified through via Parties Block using Party Role 27 which signifies Account
660	AcctIDSource
581	AccountType		Type of account associated with the order (Origin). Account may also be specified through via Parties Block using Party Role 27 which signifies Account
	Instrument
15	Currency
730	SettlPrice
731	SettlPriceType		Values = Final, Theoretical
734	PriorSettlPrice
573	MatchStatus		Used to indicate if a Position Report is matched or unmatched
	InstrmtLegGrp		Specifies the number of legs that make up the Security
	PosUndInstrmtGrp		Specifies the number of underlying legs that make up the Security
	PositionQty		Insert here the set of "Position Qty" fields defined in "Common Components of Application Messages"
	PositionAmountData		Insert here the set of "Position Amount Data" fields defined in "Common Components of Application Messages"
506	RegistStatus		RegNonRegInd
743	DeliveryDate
1434	ModelType
811	PriceDelta
58	Text
354	EncodedTextLen		Must be set if EncodedText field is specified and must immediately precede it.
355	EncodedText		Encoded (non-ASCII characters) representation of the Text field in the encoded format specified via the MessageEncoding field.
	StandardTrailer	x

Notes

Error in FIX Specification:

Comment for field 715 ClearingBusinessDate says "The Clearing Business Date referred to by this maintenance request" but this is not a maintenance request.

Error in FIX Specification:

Comment for component PosUndInstrmntGrp says "Specifies the number of underlying legs that make up the Security" but this should be about the underlying securities of the instrument component.