How to send Blob using Dio in flutter

Question

Im making a flutter app from an legacy app made in JS.

the legacy app sends pictures that way:

async createNewMaintenanceService(data: {
    areaType: MaintenanceArea;
    type: MaintenanceType;
    comments: string;
    area?: Area;
    photo?: Blob;
    subcategory?: IssueType;
    period?: MaintenancePeriod;
    unattendedAccessAllowed?: boolean;
  }): Promise<any> {
    console.log('TCL: MaintenanceService -> constructor -> data', data);
    const formData = new FormData();

    formData.append('areaType', data.areaType);
    formData.append('comments', data.comments);
    formData.append('type', data.type);

    if (data.area) {
      formData.append('area', String(data.area.id));
    }

    if (data.photo) {
      formData.append('file', data.photo);
    }

    if (data.subcategory) {
      formData.append('subcategory', String(data.subcategory.id));
    }

    if (data.period) {
      formData.append('suggestedServicePeriod', data.period);
    }

    if (data.unattendedAccessAllowed) {
      formData.append('unattendedAccessAllowed', String(data.unattendedAccessAllowed ? 1 : 0));
    }

    console.log('TCL: MaintenanceService -> constructor -> formData', formData);

    return await this.API.post('/maintenances', formData, {
      tokenRequired: true,
    });
  }

In flutter, im doing it like that:

// *** state.imageFile is a File()***

// *** this is the data i'm sending :
final data = {
          'areaType': area,
          'comments': commentController.text,
          'period': period,
          'AccessAllowed': isAuthorizedAccess,
          'file': imageFile, // here im having problems
            }..removeWhere((key, value) => value == null);



  Future<Either<CreateMaintenanceException, dynamic>> createNewMaintenance(
    Map<String, dynamic> data,
  ) async {
    try {
      final result = await _client.post(
        isTokenRequired: true,
        path: '/maintenances',
        data: data,
      );

      return Right(
        result,
      );
    } on DioException catch (e) {
      return Left(
        CreateMaintenanceException(e.response?.data),
      );
    }
  }

I can do the req if i send image as null (not sending), but i'm having problems sending that imageFile.

I already tried to convert imageFile and send inside data that way:

 Future<String> toBase64() async {
    final path = this.path;

    final List<int> imageBytes = await File(path).readAsBytes();
    return base64Encode(imageBytes);
  }

imageFile!.toBase64()

and like that:

 Future<List<int>> toBlob() async {
    final path = this.path;

    final List<int> imageBytes = await File(path).readAsBytes();
    return imageBytes;
  }

imageFile!.toBlob()

but no one worked.

What am I doing wrong?