> ## Documentation Index
> Fetch the complete documentation index at: https://docs.cdp.coinbase.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Derivatives FIX Header/Trailer Messages

All FIX messages (administrative and business) require a [Standard Header](#standard-header) and [Standard Trailer](#standard-trailer) component.

## Standard Header

| Tag | Name                   | FIX Type         | Req | Description                                                                                                                                                                                                                                                                                |
| :-- | :--------------------- | :--------------- | :-- | :----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| 8   | BeginString            | String(7)        | Y   | FIX version for session, e.g., `FIX.4.4`.                                                                                                                                                                                                                                                  |
| 9   | BodyLength             | Int(6)           | Y   | Number of bytes in the message body.                                                                                                                                                                                                                                                       |
| 35  | MsgType                | String(2)        | Y   | FIX message type.                                                                                                                                                                                                                                                                          |
| 34  | MsgSeqNum              | Int(9)           | Y   | Message sequence number.                                                                                                                                                                                                                                                                   |
| 43  | PossDupFlag            | Boolean(1)       | N   | Flag that represents whether or not the message may have been retransmitted with this sequence number. Must be `Y` for messages sent in response to a Resend Request from the exchange.                                                                                                    |
| 49  | SenderCompID           | String(6)        | Y   | Consists of SubFirmID and SessionID. SubFirmID is left-most 3 chars. SessionID is right-most 3 chars. Example: `EBR123` <br /><br />To Exchange: Connection ID assigned by Coinbase Derivatives Exchange. <br /><br /> From Exchange: Value from order entry tag 56, TargetCompID: `COIND` |
| 50  | SenderSubID            | String(18)       | Y   | Unique identifier for the end trader submitting orders, issued by an exchange clearing member firm (clearing member), their contracted vendors, or assignees                                                                                                                               |
| 116 | OnBehalfOfSubID        | String(18)       | N   | Can be used to identify the end trader submitting orders if SenderSubID (50) is populated by a third party connection provider.                                                                                                                                                            |
| 52  | SendingTime            | UTCTimestamp(21) | Y   | Time the message was transmitted, expressed in UTC, microseconds: `YYYYMMDD-HH:MM:SS.ssssss`.                                                                                                                                                                                              |
| 56  | TargetCompID           | String(7)        | Y   | To Exchange: ID of entity receiving the message: `COIND` <br /><br />From Exchange: Value from order entry SenderCompID (49), example: `EBR123`                                                                                                                                            |
| 57  | TargetSubID            | String(20)       | Y   | To Exchange: ID of destination exchange system: PROD or TEST <br /><br />From Exchange: Echo back TargetSubID (57) sent by client system                                                                                                                                                   |
| 122 | OrigSendingTime        | UTCTimestamp(21) | C   | For resent messages only, contains timestamp from SendingTime (52) from original message.                                                                                                                                                                                                  |
| 369 | LastMsgSeqNumProcessed | Int(9)           | N   | MsgSeqNum (34) of the last message from the client received and processed by the gateway.                                                                                                                                                                                                  |

## Standard Trailer

| Tag | Name     | FIX Type  | Req | Description                                                              |
| :-- | :------- | :-------- | :-- | :----------------------------------------------------------------------- |
| 10  | CheckSum | String(3) | Y   | Always the last tag in a message. Functions as end-of-message delimiter. |