CORS not working with AWS SAM

Hi everyone,

I setup CORS using SAM a few weeks ago and it was working fine until I today. Now, I keep getting Access to XMLHttpRequest at 'abc' from origin 'xyz' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. I have this in my template.yaml file:

Globals:
  Api:
    Cors:
      AllowMethods: "'GET,POST,OPTIONS'"
      AllowHeaders: "'Content-Type'"
      AllowOrigin: "'*'"

and in my lambda function, I'm returning the the headers like so:

return {
        "statusCode": 200,
        'headers': {
            'Access-Control-Allow-Headers': 'Content-Type',
            'Access-Control-Allow-Origin': '*',
            'Access-Control-Allow-Methods': 'OPTIONS,GET'
        },
        "body": json.dumps(
            {
                "message": response,
            }
        ),
    }

but I'm still getting Access to XMLHttpRequest at 'abc' from origin 'xyz' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. any time I try to hit that API from the frontend.

I also tried manually enabling CORS from the API Gateway, but it threw unspecified errors.

From reading other support posts, I thought maybe adding a 200 method response on the gateway would fix it, but that didn't change anything either, even after adding a model for the response with an accurate schema.

I didn't change anything with the headers so I don't know why it stopped working. I also tried clearing my cache and running from an incognito window to make sure my browser cache wasn't messing with anything. Any help would be much appreciated.

Edit: I forgot to mention, this API works fine when I run it locally using sam local start-api. It only throws this error when it is deployed.