Error: Error executing "ListBuckets" on Amazon s3 using w3tc plugin for wordpress

Question

I was trying to use the the W3TC plugin for Wordpress in order to use Amazon S3 as storage for my files.

Had no problem (well, after a little headscratching anyway) creating a new IAM user and getting the connection from the plugin to S3 - however when I clicked on "Test S3 Upload" it came back with the following error:

Error: Error executing "ListBuckets" on "https://s3.eu-west-2.amazonaws.com/"; AWS HTTP error: Client error: `GET https://s3.eu-west-2.amazonaws.com/` resulted in a `403 Forbidden` response: AccessDeniedAccess Denied3G27GE (truncated...) AccessDenied (client): Access Denied - AccessDeniedAccess Denied

The IAM user had the following policy attached, which is the standard policy given in pretty much all examples I could find online of how to set up a user which allows uploads to an s3 bucket:

    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "s3:CreateBucket",
                "s3:DeleteObject",
                "s3:Put*",
                "s3:Get*",
                "s3:List*"
            ],
            "Resource": [
                "arn:aws:s3:::com.fatpigeons.fatpigeons-object-storage",
                "arn:aws:s3:::com.fatpigeons.fatpigeons-object-storage/*"
            ]
        }
    ]
}```

Answer 1

It seems that the "Test S3 Upload" button was trying to search for my bucket, rather than going directly there.

Allowing the IAM user to list all of my buckets at a level above the bucket itself using the following code solved the problem:

    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "s3:CreateBucket",
                "s3:DeleteObject",
                "s3:Put*",
                "s3:Get*",
                "s3:List*"
            ],
            "Resource": [
                "arn:aws:s3:::com.fatpigeons.fatpigeons-object-storage",
                "arn:aws:s3:::com.fatpigeons.fatpigeons-object-storage/*"
            ]
        },
        {
            "Effect": "Allow",
            "Action": [
                "s3:ListAllMyBuckets"
            ],
            "Resource": [
                "arn:aws:s3:::*"
            ]
        }
    ]
}```