HITs - MTurk Workers Upload Problem with AWS

Hello,

I tried to do everything in this tutorial: https://blog.mturk.com/tutorial-how-to-create-hits-that-ask-workers-to-upload-files-using-amazon-cognito-and-amazon-s3-38acb1108633

But in the end, when the MTurk workers try to upload their work, they get this message: "Failed to upload. Please contact the Requester."

I don't know what is the problem. Please help.