AWS S3 storage does not give a valid URL after uploading file

Question

I am new to AWS. I use Amplify to upload a video file to S3 storage using Flutter. I want to get the URL after uploading a video to use it elsewhere. I use Amplify.Storage.getUrl(key)).url to get the URL. But when I want to go to the link via the browser, it shows the following error there:

This XML file does not appear to have any style information associated with it. The document tree is shown below.
<Error>
    <Code>AccessDenied</Code>
    <Message>No AWSAccessKey was presented.</Message>
    <RequestId>AK49EW70AR8N1NVC</RequestId>
    <HostId>Z6FBLU/GABRvJKFX827m3HoIKfVIpU0iXmH3gwSpcu04nNiqqEFjHZGGLn3VyyVNMY7ndK541ro= 
    </HostId>
</Error>

And also this link doesn't work when I want to play a video using VideoPlayerController.network(videoUrl). So what is the solution to get a general URL for the video file uploaded that can be used elsewhere? Thanks in advance.