Payload is empty when using IAmazonLambda.InvokeAsync in the AWS .NET SDK

Question

So I'm using Unity (c#) to implement client-sided integration with Lambda and have imported the AWS .NET SDK (2.0-3.7.200.0) into Unity.

I'm trying to invoke a simple function on Lambda using the SDK, but when I do, the Playload of the response is completely empty. I get no errors or exceptions and the response comes back fine, only I expect to receive the return value of the handler function, but get nothing.

---

"TestingFunction" on AWS Lambda (index.js):

exports.handler = async (event) => {
    
    let response = {
        Success: true,
        Result: "Hello from Lambda!"
    };

    return response;
};

---

My c# Code for invoking the function:

AWSCredentials Credentials = new CognitoAWSCredentials(IdentityPoolId, RegionEndpoint.GetBySystemName(CognitoIdentityRegion));
IAmazonLambda Client = new AmazonLambdaClient(Credentials, RegionEndpoint.GetBySystemName(LambdaRegion));

public void Invoke()
{
    ResultText.text = "Invoking 'TestingFunction' function in Lambda... \n";
    InvokeRequest invokeRequest = new InvokeRequest() {
        FunctionName = "TestingFunction",
        Payload = "",
        InvocationType = InvocationType.Event
    };
    
    WaitForFunctionInvoke(invokeRequest, m_FunctionInvokeCallback);
}

// Asynchronous function for waiting for function invoke
async void WaitForFunctionInvoke(InvokeRequest request, InvokeFunctionCallback callback)
{
    InvokeResponse response = await Client.InvokeAsync(request);

    ResultText.text += "\nInvoke Response Received! Invoking callback function..." + "\n";
    callback.Invoke(response);
}

// Invoke Function Callback
void OnFunctionInvokeReceived(InvokeResponse response)
{
    byte[] responseByteArray = response.Payload.ToArray();
    string payloadString = Encoding.ASCII.GetString(responseByteArray);
    ResultText.text += "Playload: " + payloadString + "\n";
}

---

I believe I've setup the AWS sided requirements such as:

• Created a new Cognito Identity Pool for initializing credentials (identity pool id).
• Added all the necessary Permission Policies to the IAM role associated with my identity pool.

I've also used the same c# design for Listing all current Lambda functions, using IAmazonLambda.ListFunctionsAsync(), and that works completely fine.

Any ideas on why the response for the function invoke has no payload?