microsoft/autogen · error · NotSupportedException

Message type {m.GetType()} is not supported.

Error message

Message type {m.GetType()} is not supported.

What it means

Thrown by GeminiChatAgent.BuildChatRequest when a message in the conversation is not an IMessage<Content> (the Gemini-native content envelope). AutoGen's Gemini agent does not convert arbitrary message types, so any TextMessage/ToolCallMessage sent raw into GeminiChatAgent triggers NotSupportedException with the offending CLR type name.

Source

Thrown at dotnet/src/AutoGen.Gemini/GeminiChatAgent.cs:162

    }

    public async IAsyncEnumerable<IMessage> GenerateStreamingReplyAsync(IEnumerable<IMessage> messages, GenerateReplyOptions? options = null, [EnumeratorCancellation] CancellationToken cancellationToken = default)
    {
        var request = BuildChatRequest(messages, options);
        var response = this.client.GenerateContentStreamAsync(request);

        await foreach (var item in response.WithCancellation(cancellationToken).ConfigureAwait(false))
        {
            yield return MessageEnvelope.Create(item, this.Name);
        }
    }

    private GenerateContentRequest BuildChatRequest(IEnumerable<IMessage> messages, GenerateReplyOptions? options)
    {
        var geminiMessages = messages.Select(m => m switch
        {
            IMessage<Content> contentMessage => contentMessage.Content,
            _ => throw new NotSupportedException($"Message type {m.GetType()} is not supported.")
        });

        // there are several rules applies to the messages that can be sent to Gemini in a multi-turn chat
        // - The first message must be from the user or function
        // - The (user|model) roles must alternate e.g. (user, model, user, model, ...)
        // - The last message must be from the user or function

        // check if the first message is from the user
        if (geminiMessages.FirstOrDefault()?.Role != "user" && geminiMessages.FirstOrDefault()?.Role != "function")
        {
            throw new ArgumentException("The first message must be from the user or function", nameof(messages));
        }

        // check if the last message is from the user
        if (geminiMessages.LastOrDefault()?.Role != "user" && geminiMessages.LastOrDefault()?.Role != "function")
        {
            throw new ArgumentException("The last message must be from the user or function", nameof(messages));
        }

View on GitHub (pinned to 027ecf0a37)

Solutions

1. Register GeminiMessageConnector middleware on the Gemini agent so messages are converted to IMessage<Content> before the request is built (use the Gemini agent creation helper which does this for you)
2. If you build GeminiChatAgent manually, wrap payloads yourself in MessageEnvelope.Create(Content, from)
3. In multi-provider chats, insert the appropriate provider connector middleware on each agent

Example fix

// before:
var agent = new GeminiChatAgent(...);
await agent.GenerateReplyAsync(new[] { new TextMessage(Role.User, "hi") }); // throws
// after:
var agent = new GeminiChatAgent(...)
    .RegisterMessageConnector(); // GeminiMessageConnector converts TextMessage -> Content

// Verify every outgoing message is Gemini-native before calling the raw agent
if (messages.Any(m => m is not IMessage<Content>))
    messages = ConvertViaConnector(messages); // or ensure connector middleware is registered

static bool AllGeminiNative(IEnumerable<IMessage> msgs) =>
    msgs.All(m => m is IMessage<Content>);

try { return await geminiAgent.GenerateReplyAsync(messages, options, ct); }
catch (NotSupportedException e) when (e.Message.Contains("not supported"))
{ /* register GeminiMessageConnector on the agent and retry */ }

When it happens

Trigger: Sending messages (TextMessage, ToolCallMessage, ImageMessage, or custom IMessage) directly to GeminiChatAgent.GenerateReplyAsync without the GeminiMessageConnector middleware in the pipeline.

Common situations: Using the low-level GeminiChatAgent instead of the factory helper that registers GeminiMessageConnector; mixing agents from different providers in one chat and forwarding their replies verbatim to Gemini; upgrades where connector registration moved from implicit to explicit.

Related errors

• Unsupported message type: {reply.GetType()}
• No user message found.
• No user message found.
• The first message is ToolCallMessage, but the update message
• FunctionMap is not available

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/e37eaeaa82a21432. Report an issue: GitHub.