Returns one webhook subscription on your account as a one-element array. An ID that belongs to another account is treated exactly like one that does not exist and is answered with 404. The single-subscription read names fields slightly differently from the list: the name is name here and webhook_name in the list, and the HTTP method is request_type here and webhook_req_type there. header_json is returned in clear, so treat the response as sensitive if you stored credentials in it.