Payment method trying to get authenticatation with restsharp

            
RestClient client = new RestClient("https://www.billplz.com");
            RestRequest request = new RestRequest("/api/v3/bills", Method.POST);
            request.AddHeader("collection_id", strColId);
            request.AddHeader("Authorization", "Basic " + strApiKey + ":");
            
            request.AddParameter("email", email);
            request.AddParameter("name", name);
            request.AddParameter("amount", amount);
            request.AddParameter("callback_url", callback_url);

            
RestClient client = new RestClient("https://www.billplz.com");
            RestRequest request = new RestRequest("/api/v3/bills", Method.POST);
            request.AddHeader("collection_id", strColId);
            request.AddHeader("Authorization", "Basic " + strApiKey + ":");
            
            request.AddParameter("email", email);
            request.AddParameter("name", name);
            request.AddParameter("amount", amount);
            request.AddParameter("callback_url", callback_url);

IRestResponse response = client.Execute(request);
var content = response.Content; // raw content as string

Install-Package RestSharp -Version 105.0.1.0