最后！！花了几个小时后，shammy 12的帖子帮助我找出了问题所在。这段时间我一直在尝试基于json格式的参数创建签名。尽管Binance US文档明确指出，
totalParams定义为query string与request body级联
这在我引用的大多数响应中都被忽略了。甚至recvWindow参数也与无效签名错误无关。我调试这个问题所用的全部时间就是找到一种方法将查询格式化为，

String _paramsString = 'timestamp=' + timeStamp.toString();

并且，这是通过使用以下来实现的：

String _paramsString = Uri(queryParameters: baseParams).query;

这里是完整的调试代码。如果有任何问题请随时告诉我。我已经重命名了一些变量，以提高可读性，避免一些可能的混乱。

import 'dart:convert';

import 'package:convert/convert.dart';
import 'package:crypto/crypto.dart';
import 'package:http/http.dart' as http;

class BinanceRestClient {
  final int timeStamp = DateTime.now().millisecondsSinceEpoch;

  Future<http.Response> getResponse({
    required String secret,
    required String apiKey,
    required String path,
    Map<String, dynamic>? queryParams,
  }) async {
    //Header
    Map<String, String> headers = {};
    headers['X-MBX-APIKEY'] = apiKey;

    //Base params include the timestamp in milliseconds since epoch
    //and query parameters required for API end point
    Map<String, dynamic> baseParams = {};
    baseParams['timestamp'] = timeStamp.toString();
    if (queryParams != null) {
      baseParams.addAll(queryParams);
    }

    //Total params is the combination of base params and signature.
    Map<String, dynamic> totalParams = baseParams;
    totalParams['signature'] = _createSignature(
      secret: secret,
      baseParams: baseParams,
    );

    final Uri uri = Uri.https('api.binance.us', path, totalParams);
    final http.Response response = await http.get(
      uri,
      headers: headers,
    );
    return response;
  }

  String _createSignature({
    required String secret,
    required Map<String, dynamic> baseParams,
  }) {
    //Important Note: baseParams must be changed to a concatenated string before hashed.
    //Failure to do so will result in signature invalid error
    //
    //i.e., String _paramsString = 'timestamp=' + timeStamp.toString();
    //
    //Following converts a json query to a concatenated string
    final String _paramsString = Uri(queryParameters: baseParams).query;
    final List<int> _message = utf8.encode(_paramsString);
    final List<int> _key = utf8.encode(secret);
    final List<int> _mac = Hmac(sha256, _key).convert(_message).bytes;
    final String _signature = hex.encode(_mac);
    return _signature;
  }
}

另一种方式在 dart （Flutter）我如何让它工作使用crypto：^3.0.2和http：^0.13.5包

test() async {

   String api = 'timestamp=${DateTime.now().millisecondsSinceEpoch}';

   var res = ApiBinance.get(context, ApiBinance.account, api);
}

二进制的API类

import 'dart:developer';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';
import 'package:crypto/crypto.dart';

class ApiBinance {

   static var base = 'https://testnet.binance.vision';
   static var account = '$base/api/v3/account?';

   static Map<String, String> headers() {

      var headers = {
        'X-MBX-APIKEY': 'API KEY',
        'Content-Type': 'application/json',
      };

      return headers;
   }

   static String signature(String queryParams) {

      List<int> messageBytes = utf8.encode(queryParams);
      List<int> key = utf8.encode('SECRET');
      Hmac hash = Hmac(sha256, key);
      Digest digest = hash.convert(messageBytes);
      // String signature = base64.encode(digest.bytes); Does not work
      // String signature = sha256.convert(digest.bytes).toString(); // does not work

      return '$digest'; // I return directly digest and it works

   }

   static Future<String?> get(BuildContext context, url, String queryParams) async {

      String sign = signature(queryParams);

      var uri = Uri.parse('$url$queryParams&signature=$sign');

      var response = await http.get(
        uri,
        headers: headers(),
      );

      if (response.statusCode == 200) {
        print(response.body);
      } else {
        print('Request failed with status: ${response.statusCode}. 
        ${response.body}');
      }

      return response.body;
  }
}