LexRuntimeV2::LexRuntimeV2Client::StartConversationAsync not generating events

We're trying to get streaming working with C++ LexRuntimeV2Client. I'm making a successful call to "PutSession," then attempting to start the stream by calling "StartConversationAsync." Code looks like this:

` LexRuntimeV2::Model::StartConversationHandler convoHandler = LexRuntimeV2::Model::StartConversationHandler();

convoHandler.SetTextResponseEventCallback(textEvent);
convoHandler.SetIntentResultEventCallback(intentEvent);
convoHandler.SetOnErrorCallback(errorEvent);
convoHandler.SetHeartbeatEventCallback(heartbeatEvent);

startConvo.WithBotId(BotId)
    .WithBotAliasId(BotAliasId)
    .WithLocaleId(Locale)
    .WithSessionId(ConvoSession)
    .WithEventStreamHandler(convoHandler)
    .WithConversationMode(Aws::LexRuntimeV2::Model::ConversationMode::TEXT);

client.StartConversationAsync(startConvo, readyHandler, responseHandler);

I'm getting a callback to "readyHandler" but none of the other callbacks are firing. I've read some sources that suggest that the issue is WinHttp client, but it's not clear how to switch to curl on Windows to test. Currently testing this on Windows, but the target deployment will be a Linux Docker container.

Documentation is very very light for this API so I may definitely be calling it incorrectly. I can successfully call "RecognizeText" on the bot and get proper results so I know the client & bot are configured properly.

Any help for how to make this call would be appreciated.