From FIXwiki

FIX Message ApplicationMessageReport (MsgType=BY)

MsgType	FIX Specification	First introduced	Deprecated
MsgType=BY	Infrastructure messages - Application	FIX.5.0

This message is used for three different purposes: to reset the ApplSeqNum (1181) of a specified ApplID (1180). to indicate that the last message has been sent for a particular ApplID, or as a keep-alive mechanism for ApplIDs with infrequent message traffic. The purpose of the Application Message Report is indicated by ApplReportType (1426).

Message Contents By FIX Version

Notes

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