I am getting an error Misused header name 'Authorization' with DocuSignClient

I am converting code from the legacy authentication to OAuth and using the new DocuSignClient in .net.  I am able to get the Access Token, but when I call the CreateEnvelope, it returns Misused header name, 'Authorization'.

My code (in VB.NET)

            Dim docuSignClient = New DocuSignClient("https://demo.docusign.net/restapi")
            docuSignClient.Configuration.AddDefaultHeader("Authorization", "Bearer " & accessToken)

            Dim envelopesApi = New EnvelopesApi(docuSignClient)

            Dim envelopeDefinition = GetEnvelopeDefinition()

            Dim results = envelopesApi.CreateEnvelope(clientID, envelopeDefinition)