Test failed but why?

I follow up this tutorial https://github.com/W3EDGE/w3-total-cache/wiki/FAQ:-CDN#how-do-i-configure-amazon-simple-storage-service-amazon-s3-or-amazon-cloudfront-as-my-cdn

but when i hit test upload, it shows a message saying test failed. but why is failing?? how can i solve the problem if i don’t know why it happen?

What is the pre requisite to conect to my amazon s3 bucket besides putting the bucket name, and the keys?

Thanks you all for all the help!