API integration with web.config

Hello! I’m new to Postman. I’m trying to integrate API with a web application and in their documentation they say that i have to add web.config file that contain:

And the example for calling method it’s looking like this:

private EFacturaApiRef.ServiceClient _client;
_client = new EFacturaApiRef.ServiceClient();
_client.ClientCredentials.UserName.UserName = “supplier”;
_client.ClientCredentials.UserName.Password = “supplier”;
string newid = Guid.NewGuid().ToString();
var request = new AcceptedRequest
SeriaAndNumbers = new List
new InvoiceIndentificator { Number = “000004664”, Seria
= “EA7A”},
new InvoiceIndentificator { Number = “000004664”, Seria
= “EAA” }
RequestId = newid
var response = _client.PostAcceptedInvoices(request);
foreach (var info in response.Results)
Console.WriteLine(info.Seria + " " + info.Number + " " +

Besides what I’ve written here I have a user and a password from API User created on their web application.

I’ve made some test on Postman, but i think i don’t have the knowledge to advance with this topic. If you can, please give me some hints of what i have to do