Getting S3 error: Domain name specified in [*********] is not a valid S3 domain when pasting S3 URL for the template from S3 bucket of a conduit account in Create Stack Tab for my account.

Thank you. It got through the first error. When I try the object URL which is of the format you suggested, I am now getting the "s3 error access denied for more information check http://docs.aws.amazon.com/amazons3/latest/api/errorresponses.html" error. What should I do at this point?

This is probably because the S3 bucket where Account1's CloudFormation template is uploaded cannot be accessed. I think this can be resolved by enabling S3 public access or setting up a cross-account IAM role.

If you want to set the S3 bucket for public access, you can use it by disabling the bucket policy and public access block settings below.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Principal": "*",
            "Action": [
                "s3:GetObject",
                "s3:GetObjectVersion"
            ],
            "Resource": "arn:aws:s3:::s3-bucket-name/*"
        }
    ]
}

When configuring cross-account settings, the following documents may be helpful. https://repost.aws/knowledge-center/cross-account-access-s3

Thank you so much! I will work on this and post updates here.