CORS question on using a REACT app with Serverless Framework

Serverless Framework
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1

I’ve seen many posts on this topic, but all of them deal with the CORS error message about missing headers and such.

I’m facing a different issue (I think…) - I’m getting a valid 200 response that looks like this:

Response {type: ‘cors’, url: ‘https://…amazonaws.com/dev/calculate’, redirected: false, status: 200, ok: true, …} body: ReadableStream bodyUsed: false headers: Headers {} ok: true redirected: false status: 200 statusText: “” type: “cors” url: “https://…amazonaws.com/dev/calculate”

The details:

I have a simple React app that uses a AWS Lambda function to calculate a sum of 2 numbers. I used Serverless to deploy this to AWS. The *.yml looks like so:

service: reactcalculatorserverless
frameworkVersion: ‘3’

provider:
name: aws
runtime: nodejs12.x

functions:
doCalculation:
handler: lambdas/doCalculation.handler
events:
- http:
path: calculate
method: POST
cors: true

The Lambda:

module.exports.handler = async (event) => {

const { operand1, operand2, operator } = JSON.parse(event.body);
let result = 0;

switch (operator)
{
    case "+":
        result = operand1 + operand2;
        break;
    case "-":
        result = operand1 - operand2;
        break;
    case "*":
    case "X":
    case "x":
        result = operand1 * operand2;
        break;
    case "/":
        result = operand1 / operand2;
        break;
}    

const responseBody = {
    "result" : result
};

const response = {
    "statusCode": 200,
    "headers": {
        "Access-Control-Allow-Origin" : "*",
        "Access-Control-Allow-Credentials": true,
    },
    "body": JSON.stringify(responseBody),
    "isBase64Encoded": false
};

return response;

Of course this all works well with Postman.

Is this a CORS error, even though it is a valid response header? Since I have “cors=true” in the yml file, it did do the right thing and added the OPTIONS in API Gateway, but still I don’t get the correct response from the Lambda.