Orchestrators.cs

[FunctionName("O_SendMessage")]
public static async Task SendMessageOrchestrator(
    [OrchestrationTrigger] DurableOrchestrationContextBase context,
    ILogger log)
{
    MessageInput messageInput = context.GetInput<MessageInput>();

    string smsKey = await context.CallActivityAsync<string>("A_SaveTwilioMapping", context.InstanceId);
    messageInput.SmsKey = smsKey;

    await context.CallActivityAsync<object>("A_SendTwilioText", messageInput);

    string status = await context.WaitForExternalEvent<string>("TwilioCallback");

    log.LogWarning($"Got status from Twilio: {status}");
}