Documentation Index
Fetch the complete documentation index at: https://docs.paxos.com/llms.txt
Use this file to discover all available pages before exploring further.
Logon
Initiate a FIX session with a Logon message — MsgType (35) set to A. Set EncryptMethod (98) to 0 and HeartBtInt (108) to the desired interval (default: 30 seconds).
Standard FIX Fields
| Tag | Field | When to Include | Notes |
|---|
8 | BeginString | Always | Standard FIX header |
9 | BodyLength | Always | Standard FIX header |
35 | MsgType | Always | A (Logon) |
49 | SenderCompID | Always | Standard FIX header |
56 | TargetCompID | Always | Standard FIX header |
34 | MsgSeqNum | Always | Standard FIX header |
52 | SendingTime | Always | Standard FIX header |
Standard FIX Trailer
| Tag | Field | When to Include | Notes |
|---|
10 | CheckSum | Always | |
Logon Fields
| Tag | Field | When to Include | Notes |
|---|
98 | EncryptMethod | Always | Must be 0 |
108 | HeartBtInt | Always | Heartbeat interval in seconds (default: 30) |
Send the Logon message to initiate the session:| Tag | Field | Value | Notes |
|---|
49 | SenderCompID | Your client ID | |
56 | TargetCompID | ITBIT_PROD / ITBIT_SANDBOX | |
Paxos responds with a matching Logon message:| Tag | Field | Value | Notes |
|---|
49 | SenderCompID | ITBIT_PROD / ITBIT_SANDBOX | |
56 | TargetCompID | Your client ID | |
Logon with Reset Sequence Number Flag
Reset sequence numbers on both sides by sending a Logon with ResetSeqNumFlag (141) set to Y.
Uses the same Standard FIX Fields and Logon Fields as a regular Logon, plus:
| Tag | Field | When to Include | Notes |
|---|
141 | ResetSeqNumFlag | Always | Y — reset sequence numbers on both sides |
Send the Logon with ResetSeqNumFlag (141) = Y.
Paxos responds with a matching Logon that also includes ResetSeqNumFlag (141) = Y.
Replay Messages
Request retransmission of messages with a Resend Request — MsgType (35) set to 2. Use this when a gap in sequence numbers is detected, a message is lost, or higher-than-expected sequence numbers arrive from the counterparty.
Resend Scenarios
| Scenario | BeginSeqNo (7) | EndSeqNo (16) |
|---|
| Single message | N | N (same value) |
| Range of messages | First in range | Last in range |
| All subsequent messages | N | 0 |
Standard FIX Fields
| Tag | Field | When to Include | Notes |
|---|
8 | BeginString | Always | Standard FIX header |
9 | BodyLength | Always | Standard FIX header |
35 | MsgType | Always | 2 (Resend Request) |
49 | SenderCompID | Always | Standard FIX header |
56 | TargetCompID | Always | Standard FIX header |
34 | MsgSeqNum | Always | Standard FIX header |
52 | SendingTime | Always | Standard FIX header |
Standard FIX Trailer
| Tag | Field | When to Include | Notes |
|---|
10 | CheckSum | Always | |
Required| Tag | Field | When to Include | Notes |
|---|
7 | BeginSeqNo | Always | First message sequence number in range |
16 | EndSeqNo | Always | Last message sequence number in range (0 for all subsequent) |
Paxos resends the requested messages sequentially. Resent messages include:Required| Tag | Field | When Present | Notes |
|---|
7 | BeginSeqNo | Always | First message sequence number in range |
16 | EndSeqNo | Always | Last message sequence number in range |
| Tag | Field | When Present | Notes |
|---|
43 | PossDupFlag | Retransmitted messages | Y — indicates possible retransmission |
122 | OrigSendingTime | Retransmitted messages | Original time of message transmission |
Heartbeat
Monitor the FIX connection with Heartbeat messages — MsgType (35) set to 0. The default HeartBtInt (108) interval is 30 seconds.
Key Behavior
- Reset the heartbeat timer after every transmitted message, not just heartbeats.
- If no data is received within the heartbeat interval, send a Test Request (MsgType
1) to verify the connection.
- Include TestReqID (
112) to match Test Requests with Heartbeat responses. Any string can be used (a timestamp is recommended).
- If no Heartbeat response arrives in a reasonable time, consider the connection lost.
Standard FIX Fields
| Tag | Field | When to Include | Notes |
|---|
8 | BeginString | Always | Standard FIX header |
9 | BodyLength | Always | Standard FIX header |
35 | MsgType | Always | 0 (Heartbeat) |
49 | SenderCompID | Always | Standard FIX header |
56 | TargetCompID | Always | Standard FIX header |
34 | MsgSeqNum | Always | Standard FIX header |
52 | SendingTime | Always | Standard FIX header |
Standard FIX Trailer
| Tag | Field | When to Include | Notes |
|---|
10 | CheckSum | Always | |
Heartbeat Fields
| Tag | Field | When to Include | Notes |
|---|
112 | TestReqID | In response to a Test Request | Echoes the TestReqID from the Test Request |
Send a Heartbeat when no message has been sent within the HeartBtInt interval, or in response to a Test Request.
Paxos responds to Test Requests with a Heartbeat containing the matching TestReqID (112).
Reject
A Reject message — MsgType (35) set to 3 — is sent when a message cannot be processed due to a session-level rule violation.
Standard FIX Fields
| Tag | Field | When Present | Notes |
|---|
8 | BeginString | Always | Standard FIX header |
9 | BodyLength | Always | Standard FIX header |
35 | MsgType | Always | 3 (Reject) |
49 | SenderCompID | Always | Standard FIX header |
56 | TargetCompID | Always | Standard FIX header |
34 | MsgSeqNum | Always | Standard FIX header |
52 | SendingTime | Always | Standard FIX header |
Standard FIX Trailer
| Tag | Field | When Present | Notes |
|---|
10 | CheckSum | Always | |
Reject Fields
Always Present
| Tag | Field | When Present | Notes |
|---|
45 | RefSeqNum | Always | Sequence number of the rejected message |
58 | Text | Always | Human-readable reason for the reject |
373 | SessionRejectReason | Always | Reject reason code |
Logout
A Logout message — MsgType (35) set to 5 — initiates or confirms FIX session termination.
Disconnection without exchanging Logout messages indicates an abnormal condition. An unsolicited Logout may indicate a connection or account issue — Text (58) contains a human-readable message. If you cannot reconnect with ResetSeqNumFlag (141) set to Y, contact Support. Standard FIX Fields
| Tag | Field | When Present | Notes |
|---|
8 | BeginString | Always | Standard FIX header |
9 | BodyLength | Always | Standard FIX header |
35 | MsgType | Always | 5 (Logout) |
49 | SenderCompID | Always | Standard FIX header |
56 | TargetCompID | Always | Standard FIX header |
34 | MsgSeqNum | Always | Standard FIX header |
52 | SendingTime | Always | Standard FIX header |
Standard FIX Trailer
| Tag | Field | When Present | Notes |
|---|
10 | CheckSum | Always | |
Logout Fields
Always Present
| Tag | Field | When Present | Notes |
|---|
58 | Text | Always | Human-readable message indicating any issues |
