1、即使是相同的短信签名与短信正文模板，也需要针对“国内文本短信”与“海外文本短信”分别申请。开始不知道，以为只要申请一次，给国外手机发短信时给api传对应的国家码就行，后来才发现需要分别申请。

2、短信服务web api响应“手机号内容频率限制”错误。这是由于在30秒内向同一手机号多次发送了相同内容的短信，这是腾讯云短信服务的默认限制——“相同内容短信对同一个手机号，30秒内发送短信条数不超过1条”，可以通过“应用配置”的“短信频率配置”修改这个限制。

3、腾讯云短信服务没有提供 .NET Core 的 SDK，我们自己实现的代码如下：

public class TencentCloudSmsService : ISmsService{    private static readonly HttpClient _httpClient =         new HttpClient { BaseAddress = new Uri("https://yun.tim.qq.com") };    private readonly string _appId;    private readonly string _appKey;    private const string SIGNATURE = "...";    private const int DOMESTIC_TEMPLATE_ID = 1234;    private const int OVERSEA_TEMPLATE_ID = 5678;    private readonly ILogger _logger;    public TencentCloudSmsService(IConfiguration conf,        ILoggerFactory loggerFactory)    {        _appId = conf["tencentCloudSms:appId"];        if (string.IsNullOrEmpty(_appId))            throw new ArgumentException($"{nameof(_appId)} must have a value");        _appKey = conf["tencentCloudSms:appKey"];        if (string.IsNullOrEmpty(_appKey))            throw new ArgumentException($"{nameof(_appKey)} must have a value");        _logger = loggerFactory.CreateLogger
     
      ();    }    public async Task
      
        SendCode(string countryCode, long mobile, int code)    {        var random = GetRandom();        var timestamp = DateTimeOffset.Now.ToUnixTimeSeconds();        var data = new        {            tel = new { nationcode = countryCode.Replace("+", ""), mobile = mobile.ToString() },            sign = SIGNATURE,            tpl_id = countryCode == "+86" ? DOMESTIC_TEMPLATE_ID : OVERSEA_TEMPLATE_ID ,            @params = new[] { code.ToString() },            sig = ComputeSignature(mobile, random, timestamp),            time = timestamp,            extend = "",            ext = ""        };        var url = $"/v5/tlssmssvr/sendsms?sdkappid={_appId}&random={random}";        _logger.LogDebug("Post to " + _httpClient.BaseAddress + url);        var response = await _httpClient.PostAsJsonAsync
       
        (url, data);        _logger.LogDebug("Post data:\n" + JsonConvert.SerializeObject(data));        response.EnsureSuccessStatusCode();        var result = await response.Content.ReadAsAsync
        
         ();        if(result.result != 0)        {            _logger.LogError($"Failed to send message to {countryCode}-{mobile}: {result.errmsg}");                            return false;        }        return true;    }    private string ComputeSignature(long mobile, int random, long timestamp)    {        var input = $"appkey={_appKey}&random={random}&time={timestamp}&mobile={mobile}";        var hasBytes = SHA256.Create().ComputeHash(Encoding.UTF8.GetBytes(input));        return string.Join("", hasBytes.Select(b => b.ToString("x2")));    }    private int GetRandom()    {        return new Random().Next(100000, 999999);    }}