FIX Error: Invalid MsgType – Explained
An invalid MsgType error occurs when tag 35 (MsgType) contains a value that is not recognized in the FIX specification or is not supported by the counterparty. Common examples include typos, unsupported message types, or version mismatches.
Root Cause
1) Typo in MsgType value, 2) Using message type not supported by counterparty, 3) FIX version mismatch, 4) Custom message types not recognized, 5) Message type field corrupted.
Broker/Exchange Action
Broker rejects with SessionRejectReason=7 (Tag not defined for this message type) or may reject the entire message if MsgType is unrecognized.
Client/Your Action
1) Verify MsgType value is correct (D=NewOrderSingle, 8=ExecutionReport, etc.), 2) Check counterparty supports the message type, 3) Verify FIX version compatibility, 4) Use standard FIX message types, 5) Validate MsgType before sending.
Example FIX Message
How FIX Doctor Detects This
FIX Doctor validates MsgType values against known message types and flags unrecognized or unsupported types.
Related Errors
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