CORS Error - HeaderDisallowedByPreflightResponse on use of React/Chrome

Question

I have an API Gateway built on AWS, with various resources & methods already properly reaching to Lambda endpoints.

As I try to make a POST request on React to the API, everything works smooth. However, GET request provides CORS Error: HeaderDisallowedByPreflightResponse when I call the function.

Final details to add:

• I tested my code on NodeJS and surprisingly the error is not generated, fetch works smooth.
• I made sure to enable CORS at Amazon API Gateway. Deployed it properly, as it works at NodeJS
• I added "Access-Control-Allow-Headers": "Origin, X-Api-Key, X-Requested-With, Content-Type, Accept, Authorization" together with other details suggested (Origin,Methods) NodeJS works smooth, React still generates same error.

What am I doing wrong? Is this a general CORS limitation, React issue, Browser issue, or something to do with my code?

My source code on React (this one generates the error):

  async function getUserGroups() {
    try {
      const response = await fetch(APIroot + "/user" + "?userID=mymail@gmail.com", {
        method: 'GET',
        headers: {
          "accept": 'application/json',
          "Access-Control-Allow-Origin": "*",
          "Access-Control-Allow-Methods": "POST, PUT, PATCH, GET, DELETE, OPTIONS",
          "Access-Control-Allow-Headers": "Origin, X-Api-Key, X-Requested-With, Content-Type, Accept, Authorization"
        },
      });

      if (!response.ok) {
        throw new Error(`Error! status: ${response.status}`);
      }

      const result = await response.json();
      console.log(result);
      return result;
    } catch (err) {
      console.log(err);
    }
  }

My source code on NodeJS (this one fetches the data):

async function getUser() {
    try {
        const response = await fetch(APIroot + "/user" + "?userID=mymail@gmail.com", {
            method: 'GET',
            headers: {
                "accept": 'application/json',
                "Access-Control-Allow-Origin": APIroot + "/user",
                "Access-Control-Allow-Methods": "GET",
                "Access-Control-Allow-Headers": "Origin, X-Api-Key, X-Requested-With, Content-Type, Accept, Authorization"
            },
        });

        if (!response.ok) {
            throw new Error(`Error! status: ${response.status}`);
        }

        const result = await response.json();
        console.log(result);
        return result;
    } catch (err) {
        console.log(err);
    }
}