The Logon <A> message authenticates a user and starts a session. It must be the first message sent by any application requesting to initiate a FIX session. A message of the same type will be sent to acknowledge the logon.

Tag	Field Name	Required	Comments
Standard Header		Yes	MsgType <35> = A
98	EncryptMethod	Yes	Method of encryption Valid values: 0 – None / other
108	HeartBtInt	Yes	Heartbeat interval in seconds. Valid values: 30 (30 seconds)
141	ResetSeqNumFlag	No	Indicates that the both sides of the FIX session should reset sequence numbers Valid values: Y – Yes, reset sequence numbers N – No (Default)
553	Username	Yes	User Id (provided during onboarding)
554	Password	Yes	Password (provided during onboarding)
1137	DefaultApplVerID	Yes*	The default version of FIX message used in this session: 9 = FIX50SP2 Required for FIX 5.0 SP2 only
Standard trailer		Yes