You are helping me build the following AI agent workflow.

## Goal
Appointment Reminder via SMS: Triggers on new bookings via webhook, validates contact info, and sends personalized SMS reminders through Twilio.

## Specification
- What it does: Receive timely appointment reminders directly on your phone whenever you book a new service. This workflow validates your contact details and instantly sends a personalized SMS notification through Twilio so you never miss an upcoming booking.
- Trigger: Triggered by an event (Event · on new appointment)
- Autonomy: Fully hands-off
- Expected setup effort: about an afternoon
- Tools/services involved:
  - n8n: Workflow orchestration and webhook handling
  - Twilio: Sending personalized SMS reminders
  - Code: Extracting and formatting appointment data from JSON payload

## Known pitfalls, handle each one explicitly in your implementation
1. Twilio requires verified sender IDs for certain countries, so add a validation step before sending messages.
2. Phone number formatting varies by region, use an E.164 normalization library to ensure compatibility.

## Reference implementation
https://n8n.io/workflows/6932 (workflow template)
Fetch and inspect this before building. If it matches my stack, adapt it;
if not, rebuild the pattern with my tools.

## Process requirements
1. Before building: ask me which of the listed tools I actually use and
   what my platform is (n8n / Make / code / other). Do not assume.
2. Adapt the pattern to my answers; do not force the reference stack.
3. Address every pitfall above; tell me how you handled each.
4. Provide a test plan I can run before letting this touch real data.
5. Ask before any step that sends messages, modifies data, or spends money.

Source: https://usecasesforagents.com/use-case/automated-appointment-reminder-via-sms/ via usecasesforagents.com