write method not work

[springeye]

call write is error
code is :

    var map = box.toMap();
    client.write("backup-${DateTime.now().millisecondsSinceEpoch}",
        Uint8List.fromList(jsonEncode(map).codeUnits));dart

error is :

[🔔 Dio] _MultiStream<List<int>> cannot be used to imply a default content-type, please set a proper content-type in the request.
         #0      ImplyContentTypeInterceptor.onRequest (package:dio/src/interceptors/imply_content_type.dart:45:36)
         #1      DioMixin.fetch.requestInterceptorWrapper.<anonymous closure>.<anonymous closure> (package:dio/src/dio_mixin.dart:409:26)
         #2      new Future.<anonymous closure> (dart:async/future.dart:256:37)
         #3      Timer._createTimer.<anonymous closure> (dart:async-patch/timer_patch.dart:18:15)
         #4      _Timer._runTimers (dart:isolate-patch/timer_impl.dart:398:19)
         #5      _Timer._handleMessage (dart:isolate-patch/timer_impl.dart:429:5)
         #6      _RawReceivePort._handleMessage (dart:isolate-patch/isolate_patch.dart:189:12)

[mostcute]

client.write("syncdata.json", Uint8List.fromList(jsonString.codeUnits));
sameproblem

[🔔 Dio] _MultiStream<List<int>> cannot be used to imply a default content-type, please set a proper content-type in the request.
         #0      ImplyContentTypeInterceptor.onRequest (package:dio/src/interceptors/imply_content_type.dart:45:36)
         #1      DioMixin.fetch.requestInterceptorWrapper.<anonymous closure>.<anonymous closure> (package:dio/src/dio_mixin.dart:409:26)
         #2      new Future.<anonymous closure> (dart:async/future.dart:256:37)
         #3      Timer._createTimer.<anonymous closure> (dart:async-patch/timer_patch.dart:18:15)
         #4      _Timer._runTimers (dart:isolate-patch/timer_impl.dart:398:19)
         #5      _Timer._handleMessage (dart:isolate-patch/timer_impl.dart:429:5)
         #6      _RawReceivePort._handleMessage (dart:isolate-patch/isolate_patch.dart:189:12)

[szuwest]

client.write("syncdata.json", Uint8List.fromList(jsonString.codeUnits)); sameproblem

[🔔 Dio] _MultiStream<List<int>> cannot be used to imply a default content-type, please set a proper content-type in the request.
         #0      ImplyContentTypeInterceptor.onRequest (package:dio/src/interceptors/imply_content_type.dart:45:36)
         #1      DioMixin.fetch.requestInterceptorWrapper.<anonymous closure>.<anonymous closure> (package:dio/src/dio_mixin.dart:409:26)
         #2      new Future.<anonymous closure> (dart:async/future.dart:256:37)
         #3      Timer._createTimer.<anonymous closure> (dart:async-patch/timer_patch.dart:18:15)
         #4      _Timer._runTimers (dart:isolate-patch/timer_impl.dart:398:19)
         #5      _Timer._handleMessage (dart:isolate-patch/timer_impl.dart:429:5)
         #6      _RawReceivePort._handleMessage (dart:isolate-patch/isolate_patch.dart:189:12)

has the same problem