How to return a file from a ASP.Net API call?

Question

I have read a number of answers, and been searching the web for the last few weeks to try and find an answer to this.

I have read: How to return a file (FileContentResult) in ASP.NET WebAPI
and: Returning binary file from controller in ASP.NET Web API

When I am debugging, it will just continuously callback, running the method over and over. When running on a server (IIS), depending on the browser, there will be a message saying This site can’t be reached, or it will download the file, but indicate that the download has faield.

The code I am using is

    <HttpGet, Route("api/Reports/Create")>
    Public Function CreateReport() As HttpResponseMessage
        Dim data = GetReportBuffer()

        'This is just for testing
        'To check that the report is created correctly
        'I can open up temp.pdf, it is fine
        Using fs As New FileStream("c:\temp\temp.pdf", FileMode.Create)
            data.CopyTo(fs)
            fs.Flush()
            fs.Close()
        End Using

        Dim result = Request.CreateResponse(HttpStatusCode.OK)
        'This should be StreamContent(data... but using this for testing
        result.Content = New StreamContent(New FileStream("c:\temp\temp.pdf", FileMode.Open))
        result.Content.Headers.ContentType = New MediaTypeHeaderValue("application/octet-stream")
        result.Content.Headers.ContentDisposition = New ContentDispositionHeaderValue("attachment") With {.FileName = $"{fllId}.{ext}"}

        Return result
    End Function

I have also tries ByteArrayContent, but the result is exactly the same. Is there anything I am not doing correctly?