It’s right in the help Utah
using Ice.Lib.RestClient;
using Ice.Tablesets;
using Ice.Common;
var restClient = new RestClientBuilder()
.UseSession(this.oTrans.CoreSession)
.Build();
var calcShipByDateContent = new RestContent(new {needByDate = new DateTime(2021, 8, 1), custNum = 3});
var getByIdResponse = restClient.Function.Post("LibraryName", "FunctionName", calcShipByDateContent , published: true);
var functionResult = getByIdResponse .GetJsonResult();
But its much more detailed in the Help.