dotnet/aspnetcore · error · Error

Invalid SequenceId for Ack message.

Error message

Invalid SequenceId for Ack message.

What it means

Thrown by JsonHubProtocol._isAckMessage when an Ack message's `sequenceId` is not of type `number`. Ack messages (part of the stateful-reconnect / sequence-id protocol extension) must carry a numeric sequenceId so the peer can acknowledge the highest contiguous message received.

Solutions

1. Confirm both client and server support the stateful-reconnect (sequence/Ack) protocol extension.
2. Inspect the Ack frame to verify sequenceId is present and numeric.
3. If a gateway is in the path, ensure it does not rewrite or drop numeric fields.

function validAck(m: any): boolean {
  return typeof m?.sequenceId === "number";
}

function isNumericSequenceId(m: any): m is { sequenceId: number } {
  return !!m && typeof m.sequenceId === "number" && Number.isFinite(m.sequenceId);
}

When it happens

Trigger: Receiving a JSON message with `type` corresponding to Ack but whose `sequenceId` is missing, a string, null, or any non-number value. This typically originates from a malformed server response or a protocol-extension version mismatch.

Common situations: Enabling stateful reconnect on the client while the server runs a version that does not support it (or vice versa), or a proxy/gateway corrupting the sequenceId field.

Related errors

• Invalid SequenceId for Sequence message.
• Error reading JSON.
• errorMessage
• Invalid input for JSON hub protocol. Expected a string.
• Invalid payload.

AI-assisted analysis of dotnet/aspnetcore@3600ca084e (2026-08-11). Data as JSON: /api/errors/a47bdbd021f637b9. Report an issue: GitHub.

Appendix: source

Thrown at src/SignalR/clients/ts/signalr/src/JsonHubProtocol.ts:123

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

    private _isCompletionMessage(message: CompletionMessage): void {
        if (message.result && message.error) {
            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 3600ca084e)