The Reject <3> message should be issued when a message is received but cannot be passed through to the application level due to a session-level rule violation. An example of when a reject may be appropriate would be the receipt of a message with invalid basic data (e.g. MsgType(35)=&) which successfully passes de-encryption, CheckSum(10) and BodyLength(9) checks. (As a rule, messages should be forwarded to the trading application for business level rejections whenever possible.)
Rejected messages should be logged and the incoming sequence number incremented.
Note: When a message is received which is garbled, cannot be parsed or fails a data integrity check, the receiving application should disregard the message. Processing of the next valid FIX message will cause detection of a sequence gap and a Resend Request<2> will be generated. Logic should be included in the FIX engine to recognize the possible infinite resend loop which may be encountered in this situation.
Generation and receipt of a Reject<3> message indicates a serious error that may be the result of faulty logic in either the sending or receiving application.
If the sending application chooses to retransmit the rejected message it should be assigned a new sequence number and sent with PossResend(97)=Y.
Whenever possible, it is strongly recommeded that the cause of the failure be described in the Text(58) field (e.g. INVALID DATA - FIELD 35).
If an application-level message received fulfills session-level rules, it should then be processed at a business message-level. If this processing detects a rule violation, a business-level reject should be issued. Many business-level messages have specific “reject” messages, which should be used. All others can be rejected at a business-level via the Business Message Reject<j> message. See for example FIX 5.0 SP2: "Business Message Reject" message.
Note that in the event a business message is received, fulfills session-level rules, however, the message cannot be communicated to the business-level processing system, a Business Message Reject<j> with BusinessRejectReason(380) = “Application not available at this time” should be issued.
Scenarios for session-level Reject:
The '^' character is used to represent SOH character.
8=FIXT.1.1^9=141^35=3^49=SellSide^56=BuySide^34=4^52=20190606-10:22:07.617^1128=9^45=5^58=Invalid Resend Request: BeginSeqNo (5) is greater than expected (3)^10=239^