From FIXwiki

FIX Message PositionReport (MsgType=AP)

MsgType	FIX Specification	First introduced	Deprecated
MsgType=AP	PostTrade messages - PositionMaintenance	FIX.4.4

The Position Report message is returned by the holder of a position in response to a Request for Position message. The purpose of the message is to report all aspects of a position and may be provided on a standing basis to report end of day positions to an owner.

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Notes

Error in FIX Specification:

The scenario diagrams in the spec for position reporting messages refer to a non existent PositionReportID field. I presume that the intention was to refer to the PosMaintRptID field.