在电子邮件中附加 PDF 文件

我需要在动态生成的电子邮件中附上收据。我无法附加 pdf 文件，它表示我路径无效。

这是我的代码：

public static IRestResponse SendConfirmationEmail(string emailaddress,string subject,string body)
{                
    RestClient client = new RestClient();
    client.BaseUrl = "https://123456";
    client.Authenticator = new HttpBasicAuthenticator("api", "key-abcdef12345huj");
    RestRequest request = new RestRequest();
    request.AddParameter("domain", "abc.com", ParameterType.UrlSegment);
    request.Resource = "{domain}/messages";
    request.AddParameter("from", "abc <abc@xyz.com>");                
    System.Net.Mail.Attachment attachment;
    attachment = new System.Net.Mail.Attachment("~/users/Receipts/abc-414.pdf");
    request.AddParameter("attachment",attachment);
    request.AddParameter("c", emailaddress);
    request.AddParameter("to", emailaddress);
    request.AddParameter("subject", subject);        
    request.AddParameter("html", body);          
    request.Method = Method.POST;
    return client.Execute(request);               
}

任何人都可以在这个问题上帮助我吗？

谢谢

attachment = new System.Net.Mail.Attachment(HttpContext.Current.Server.MapPath("~/users/Receipts/abc-414.pdf"));