1、即使是相同的短信簽名與短信正文模板，也需要針對“國內文本短信”與“海外文本短信”分別申請。開始不知道，以為只要申請一次，給國外手機發短信時給api傳對應的國家碼就行，後來才發現需要分別申請。

2、短信服務web api響應“手機號內容頻率限制”錯誤。這是由於在30秒內向同一手機號多次發送了相同內容的短信，這是騰訊雲短信服務的默認限制——“相同內容短信對同一個手機號，30秒內發送短信條數不超過1條”，可以通過“應用配置”的“短信頻率配置”修改這個限制。

3、騰訊雲短信服務沒有提供 .NET Core 的 SDK，我們自己實現的代碼如下：

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<TencentCloudSmsService>();
    }

    public async Task<bool> 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<dynamic>(url, data);
        _logger.LogDebug("Post data:\n" + JsonConvert.SerializeObject(data));
        response.EnsureSuccessStatusCode();

        var result = await response.Content.ReadAsAsync<dynamic>();
        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);
    }
}

騰訊雲短信服務使用記錄與.NET Core C#代碼分享