> ## 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.

# Coinbase Derivatives: Predictions FIX Header/Trailer Messages

All FIX messages (session and application) on the order entry, market data, and drop copy gateways require a [Standard header](#standard-header) and [Standard trailer](#standard-trailer). Differences between the gateways are in **bold**.

## Standard header

| Tag | Name | FIX Type | Req | Description |
| :- | :- | :- | :- | :- |
| 8 | BeginString | String | Y | `FIXT.1.1` |
| 9 | BodyLength | Length | Y | Message body length. |
| 35 | MsgType | String | Y | Message type. |
| 49 | SenderCompID | String | Y | On messages you send: your API key. **Market data only:** your API key or `<apiKey>.<tag>`; see [Multiple sessions per API key](/derivatives-predictions/fix/session#multiple-sessions-per-api-key). On messages you receive: **Order entry:** `CPMOE`; **Market data:** `CPMMD`; **Drop copy:** `CBPMDC`. |
| 56 | TargetCompID | String | Y | On messages you send: **Order entry:** `CPMOE`; **Market data:** `CPMMD`; **Drop copy:** `CBPMDC`. On messages you receive: your SenderCompID. |
| 34 | MsgSeqNum | SeqNum | Y | Message sequence number, starting at `1`. |
| 52 | SendingTime | UTCTimestamp | Y | UTC time the message was sent. Outbound messages use microsecond precision, except the gap fill sent in answer to a ResendRequest; see [ResendRequest (35=2)](/derivatives-predictions/fix/session#resendrequest-352). Inbound application messages must be within the [SendingTime accuracy](/derivatives-predictions/fix/session#sendingtime-accuracy) limit. |
| 43 | PossDupFlag | Boolean | C | `Y` on messages sent in answer to a [ResendRequest (35=2)](/derivatives-predictions/fix/session#resendrequest-352). **Order entry and drop copy:** set on the SequenceReset gap fill. **Market data:** set on retransmitted application messages and on the SequenceReset gap fill. |
| 97 | PossResend | Boolean | N | **Order entry and drop copy only.** `Y` on fills replayed by [EventResendRequest (35=F3)](/derivatives-predictions/fix/session#eventresendrequest-35f3). |
| 122 | OrigSendingTime | UTCTimestamp | N | Sent with `PossDupFlag (43) = Y`. **Order entry and drop copy:** on the SequenceReset gap fill, equal to `SendingTime (52)`. **Market data:** on retransmitted application messages, the original `SendingTime (52)`. Not sent on the gap fill. |
| 369 | LastMsgSeqNumProcessed | SeqNum | N | On messages you receive: `MsgSeqNum (34)` of the last message the gateway processed from you. |
| 1128 | ApplVerID | String | C | `9` = FIX 5.0 SP2. |

## Standard trailer

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