Activities.cs

[FunctionName("A_SendTwilioText")]
public static async Task SendTwilioText(
    [ActivityTrigger] MessageInput input,
    [TwilioSms] IAsyncCollector<CreateMessageOptions> message,
    ILogger log)
{
    log.LogWarning($"Twilio Activity. Sending message");

    CreateMessageOptions smsText = new CreateMessageOptions(new PhoneNumber(input.Phone))
    {
        From = new PhoneNumber(Environment.GetEnvironmentVariable("TwilioNumber")),
        Body = input.Message,
        StatusCallback = new Uri(Environment.GetEnvironmentVariable("Host") + "/api/TwilioHandler/" + input.SmsKey)
    };

    await message.AddAsync(smsText);
}