c# - Endpointnotfoundexception : active endpoint raising error sometimes -

we working on ecommerce project data fetched restfull webservices. using async-await programming model.

some services being requested using channelfactory class , since cannot have async approach using channelfactory nor webservice provides us, using different approach shown below.

var customerlocationtask = task.run(() => new orderservice().getcustomerlocation(customerid)); var customercountrytask = this.cmscustomercountrycode(customerid);  await task.whenall(customerlocationtask, customercountrytask); 

here, requesting 2 webservices in unnatural async approach , our webservice being called in synchronous fashion using channelfactory. , code cmscustomercountrycode is:

public async task<string> cmscustomercountrycode(string customerid)     {         orderservice orderservice = new orderservice();         customer customer = await task.run(() => orderservice.getcustomer(customerid, responseformat.json));         return customer.billtoaddress.country;     } 

the issues here endpointnotfoundexception in cmscustomercountrycode method. network issue or our async approach not correct ?