I want to add header with access_token for flutter upload image

Can you try to add headers like below

Map<String, String> headers = { "Accesstoken": "access_token"};

final multipartRequest = new http.MultipartRequest('POST', Uri.parse(apiUrl))
multipartRequest.headers.addAll(headers);
multipartRequest.files.add(..)

  var request = http.MultipartRequest(
    "POST",
    Uri.parse(
      "${Urls().url}/support/tenant/register",
    ),
  );
  //add text fields
  
  request.headers["authorization"]=userToken;

  request.fields["type"] = type;
  request.fields["note"] = note;
  for (var item in path) {
    var ext = item.split('.').last;
    var pic = await http.MultipartFile.fromPath("images", item, contentType: MediaType('image', ext));
    request.files.add(pic);
  }

  //add multipart to request

  var response = await request.send();
  var responseData = await response.stream.toBytes();
  var responseString = String.fromCharCodes(responseData);

  var d = jsonDecode(responseString);