dotnet/aspnetcore · error · Error

Invalid SequenceId for Sequence message.

Error message

Invalid SequenceId for Sequence message.

What it means

A Sequence message (type 9) lets the sender resynchronize the receive window with a numeric `sequenceId`. A non-numeric value defeats the resynchronization and is rejected, mirroring the Ack validation.

Source

Thrown at src/SignalR/clients/ts/signalr/src/JsonHubProtocol.ts:129

            throw new Error("Invalid payload for Completion message.");
        }

        if (!message.result && message.error) {
            this._assertNotEmptyString(message.error, "Invalid payload for Completion message.");
        }

        this._assertNotEmptyString(message.invocationId, "Invalid payload for Completion message.");
    }

    private _isAckMessage(message: AckMessage): void {
        if (typeof message.sequenceId !== 'number') {
            throw new Error("Invalid SequenceId for Ack message.");
        }
    }

    private _isSequenceMessage(message: SequenceMessage): void {
        if (typeof message.sequenceId !== 'number') {
            throw new Error("Invalid SequenceId for Sequence message.");
        }
    }

    private _assertNotEmptyString(value: any, errorMessage: string): void {
        if (typeof value !== "string" || value === "") {
            throw new Error(errorMessage);
        }
    }
}

View on GitHub (pinned to 294cab2f9b)

Solutions

1. Verify sequenceId is emitted as a JSON number by the server.
2. Align client and server SignalR versions so the reliable-session extension is consistently implemented.
3. Turn off reliable sessions if either side cannot honor them correctly.
4. Log the raw message (logMessageContent:true) to inspect the field type.

Example fix

// before
{ "type": 9, "sequenceId": null }

// after
{ "type": 9, "sequenceId": 100 }

function validSequence(m: any): boolean {
  return m?.type === 9 && typeof m.sequenceId === 'number';
}

function isSequenceMessage(m: any): m is { type: 9; sequenceId: number } {
  return m?.type === 9 && typeof m.sequenceId === 'number';
}

When it happens

Trigger: Server sends {"type":9,"sequenceId":null} or a string sequenceId while reliable sessions are active. Caused by version skew or a server bug in the reliable-transport extension.

Common situations: One party negotiates the reliable feature but emits malformed Sequence messages; mixed old/new SignalR packages across a deployment.

Related errors

• Invalid SequenceId for Ack message.
• Invalid input for JSON hub protocol. Expected a string.
• Invalid payload.
• Invalid payload for StreamItem message.
• Invalid payload for Completion message.

AI-assisted analysis of dotnet/aspnetcore@294cab2f9b (2026-08-06). Data as JSON: /api/errors/948d3cb133103d97. Report an issue: GitHub.