VaultSharp: AWS IAM authentication does not work

I’ve tried many things to get AWS IAM role authentication to work and every time I get the error from vault:

{"errors":["didn't supply required authentication values"]}

Here is what I have that I think should work but get the above error:

var requestHeader = Convert.ToBase64String(Encoding.UTF8.GetBytes("{\"X-Vault-AWS-IAM-Server-ID\":[\"vault.example.com\"]}"));
var authMethod = new IAMAWSAuthMethodInfo(roleName: "my-role", requestHeaders: requestHeader);

I also didn’t see an included example of this.

Here is a snippet in python/ruby where people report works for AWS IAM auth - https://gist.github.com/joelthompson/378cbe449d541debf771f5a6a171c5ed#file-vault_aws_auth_py3-py

Using the vault CLI I am able to auth:

vault auth -method=aws -token-only header_value=vault.example.com role=my-role