无法使用PHP AWS SDK访问Amazon Web Services上的S3存储桶

I am trying to use the listbuckets method on aws S3 api and keep getting and error saying that my S3client object is undefined ERROR- Undefined variable: s3client in C:\XAMPPmy\htdocs.. Not sure why but any help would be awesome. I am trying to use the listbuckets method on aw