I was working on implementing file uploads to S3 in a React project. One of the setup steps is to implement a cross-border CORS configuration. Here's how you get this done.

1. Login to your S3 console.
2. Go to the bucket.
4. Select permissions.
6. Scroll down to Cross-origin resource sharing (CORS).
8. Click Edit and add this JSON array.

[  {
    "AllowedHeaders": [
      "*"
    ],
    "AllowedMethods": [
       "GET",
       "HEAD",       "PUT",
       "POST"
    ],
    "AllowedOrigins": [
       "*"
    ],
    "ExposeHeaders": [],
    "MaxAgeSeconds": 3000
  }
]

There's a good explanation of this here.