How to access rest API with a pfx certificate

var client = new RestClient("https://example.com/DataService/CustomerData/GetCustomerActivityDailySummary");
ServicePointManager.Expect100Continue = true;
ServicePointManager.DefaultConnectionLimit = 9999;
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
var certFile = Path.Combine(@"D:\myproject\", "certificate1.pfx");
X509Certificate2 certificate = new X509Certificate2(certFile, "12345678)");
client.ClientCertificates = new X509CertificateCollection() { certificate };
client.Proxy = new WebProxy();
var restrequest = new RestRequest(Method.POST);
restrequest.AddHeader("Cache-Control", "no-cache");
restrequest.AddHeader("Accept", "application/json");
restrequest.AddHeader("Content-Type", "application/json");
restrequest.AddParameter("here i have added the request parameter",ParameterType.RequestBody);
IRestResponse response = client.Execute(restrequest);