JSON文本不是以数组或对象和选项开头，以允许未设置的片段无法获得响应

Question

当我打算使用xe货币转换器api转换货币但没有得到回复时

预期的响应应该像

  

{＆＃34;术语＃34;：＆＃34; http://www.xe.com/legal/dfs.php＆＃34;＆＃34;隐私＆＃34;：＆＃34; http://www.xe.com/privacy.php＆＃34 ;, ＆＃34;从＆＃34;：＆＃34; USD＆＃34;＆＃34;量＆＃34;：1.0，＆＃34;时间戳＆＃34;：＆＃34; 2016-03-18T06：22： 00Z＆＃34;＆＃34;至＆＃34;：[{＆＃34; quotecurrency＆＃34;：＆＃34; INR＆＃34;＆＃34;中间＆＃34;：66.6094587811}]}

我在回复时收到以下错误：

  

错误：错误域= NSCocoaErrorDomain代码= 3840＆＃34; JSON文本没有以数组或对象开头，并且选项允许未设置片段。＆＃34; UserInfo = {NSDebugDescription = JSON文本不以数组或对象开头，并且选项允许未设置片段。，NSUnderlyingError = 0x7fa879f70190 {错误域= AFNetworkingErrorDomain代码= -1011＆＃34;请求失败：未找到（404）＆＃34 ; UserInfo = -
  {AFNetworkingOperationFailingURLResponseErrorKey = {URL：xecdapi.xe.com/v1/convert_from？ } {status code：404，headers {Connection =＆＃34; keep-alive＆＃34 ;; ＆＃34; Content-Length的＆＃34; = 9; ＆＃34;内容类型＆＃34; =＆＃34; text / plain;字符集= UTF-8＆＃34 ;; ，NSLocalizedDescription =请求失败：未找到（404），NSErrorFailingURLKey = xecdapi.xe.com / v1 / convert_from？}}}

我的代码是：

AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
manager.responseSerializer = [AFJSONResponseSerializer serializer];
AFJSONResponseSerializer *jsonResponseSerializer = [AFJSONResponseSerializer serializer];
NSMutableSet *jsonAcceptableContentTypes = [NSMutableSet setWithSet:jsonResponseSerializer.acceptableContentTypes];
[jsonAcceptableContentTypes addObject:@"text/plain"];
jsonResponseSerializer.acceptableContentTypes = jsonAcceptableContentTypes;
manager.responseSerializer = jsonResponseSerializer;
[manager.requestSerializer setValue:@“xxxxxxxxninternationalfze988134762" forHTTPHeaderField:@"User Name"];
[manager.requestSerializer setValue:@“xxxxqngksq5nuqmmf7tjgcihak" forHTTPHeaderField:@"Password"];
NSMutableDictionary *params = [[NSMutableDictionary alloc]init];
[params setObject:@"USD" forKey:@"from"];
[params setObject:@"INR" forKey:@"to"];