Even if you have configured an S3 bucket for static website hosting, you still have to define the correct permissions or you'll get a 403 Access Denied error. It seems like AWS could make this a lot simpler, but they don't, so here's the template. (Note the placeholder names.)
For more details see this documentation.
"{ 'Version':'2012-10-17', 'Statement':[{ 'Sid':'PublicReadGetObject', 'Effect':'Allow', 'Principal': '*', 'Action':['s3:GetObject'], 'Resource':['arn:aws:s3:::example-bucket/*' ] } ] }"