I'm follwoing this example page to create an AWS IAM Role:

https://aws.amazon.com/premiumsupport/knowledge-center/iam-assume-role-cli/

And have created this:

{
    "Version": "2012-10-17",
    "Statement": {
        "Effect": "Allow",
        "Principal": { "AWS": "arn:aws:iam::123456789012:role/example2" },
        "Action": "sts:AssumeRole"
    }
}

But when I run this cli command, the document always fails:

aws iam create-role --role-name example-role --assume-role-policy-document file://example-role-trust-policy.json

My understanding is that I'm attaching an IAM Role trust relationship to an IAM Role. This way a user, Bob, can assume an IAM Role to run certain commands. And this way I don't have to use IAM Access / Secret keys for said commands.

I apologize if this is a dumb question... but I'm unsure why this policy document keeps breaking.