If you're using RestSharp in Specflow, you can make the first API call and store the ID in a variable. Then, you can use that variable in the second API call. Here's an example of how you might do this:
var client = new RestClient("https://www.example.com/api/");
var request = new RestRequest(Method.GET);
IRestResponse response = client.Execute(request);
var id = response.Data.id;
var client = new RestClient("https://www.example.com/api/" + id);
var request = new RestRequest(Method.GET);
IRestResponse response = client.Execute(request);
This will make the two API calls in the correct order, with the second API call using the ID obtained from the first API call.