API v2 upload file with DBFILESWriteModeAdd not working

Hello,

I am using API v2 iOS sdk for upload files from my device. I want to add new files every time is file already exist. thats why i am using DBFILESWriteModeAdd for upload. But its not create new fileor even replace. I got success message after upload. Here is my code.

DBUserClient *client = [DBClientsManager authorizedClient];
DBFILESWriteMode *mode = [[DBFILESWriteMode alloc] initWithOverwrite];
NSString *destDir = @"/text.m4a"
DBUploadTask *restClient = [[[client.filesRoutes uploadData:destDir
                                               mode:mode
                                         autorename:@(YES)
                                     clientModified:nil
                                               mute:@(NO)
                                          inputData:fileData]
                     setResponseBlock:^(DBFILESFileMetadata *result, DBFILESUploadError *routeError, DBRequestError *networkError) {
                         if (result)
                         {
                         }
                         else
                         {
                         }
                     }] setProgressBlock:^(int64_t bytesUploaded, int64_t totalBytesUploaded, int64_t totalBytesExpectedToUploaded)
                        {
                        });
                     }];