TelegramGatewayNet

dotnet add package TelegramGatewayNet

using TelegramGatewayNet;
using TelegramGatewayNet.Requests;

using var client = new TelegramGatewayClient("YOUR_GATEWAY_API_TOKEN");

var result = await client.SendVerificationMessageAsync(
    new SendVerificationMessageRequest("+391234567890")
    {
        CodeLength = 6,
        Ttl = 60,
        CallbackUrl = "https://my.webhook/auth",
    });

if (result.Ok)
    Console.WriteLine(result.Value.RequestId);
else
    Console.WriteLine($"Could not send: {result.Error}");