C# AWS上托管的Alexa.NET-Outputspeech返回空白

我正在尝试创造一种技能，可以从谷歌表格中读取数据，并从我的每月预算中获得一些价值。我以前做过技能，已经有一段时间了-我在AWS Lambda上创建了一个新函数，但我无法在OutputSpeech中显示任何内容。我已经将代码回滚到使用GitHub的示例代码时，仍然没有得到响应

        public SkillResponse FunctionHandler(SkillResponse input, ILambdaContext context)
        {
            var speech = new SsmlOutputSpeech();
            speech.Ssml = "<speak>Today is <say-as interpret-as=\"date\">????0922</say-as>.</speak>";

            // create the reprompt speech
            var repromptMessage = new PlainTextOutputSpeech();
            repromptMessage.Text = "Would you like to know what tomorrow is?";

            // create the reprompt object
            var repromptBody = new Reprompt();
            repromptBody.OutputSpeech = repromptMessage;

            // create the response
            var responseBody = new ResponseBody();
            responseBody.OutputSpeech = speech;
            responseBody.ShouldEndSession = false; // this triggers the reprompt
            responseBody.Reprompt = repromptBody;
            responseBody.Card = new SimpleCard { Title = "Test", Content = "Testing Alexa" };

            var skillResponse = new SkillResponse();
            skillResponse.Response = responseBody;
            skillResponse.Version = "1.0";

            return skillResponse;

Alexa开发者控制台上的响应：

"request": {
        "type": "SessionEndedRequest",
        "requestId": "amzn1.echo-api.request.9a4f617b-5548-4e5c-a8f0-3c1853c5ad64",
        "timestamp": "2020-11-15T23:44:57Z",
        "locale": "en-US",
        "reason": "ERROR",
        "error": {
            "type": "INVALID_RESPONSE",
            "message": "SpeechletResponse was null"
        }
    }

我在Visual Studio 2019中使用以下软件包：

• Alexa.Net
• Amazon.Lambda.Core
• Amazon.Lambda.Serialization.SystemTextJson

我错过了什么

"request": {
        "type": "SessionEndedRequest",
        "requestId": "amzn1.echo-api.request.9a4f617b-5548-4e5c-a8f0-3c1853c5ad64",
        "timestamp": "2020-11-15T23:44:57Z",
        "locale": "en-US",
        "reason": "ERROR",
        "error": {
            "type": "INVALID_RESPONSE",
            "message": "SpeechletResponse was null"
        }
    }