You are helping me build the following AI agent workflow.

## Goal
Tour Payment Reminders: Twice daily, it scans for payments due in three days and sends personalized email or WhatsApp reminders with secure links.

## Specification
- What it does: You receive timely, personalized payment reminders for travelers due within three days via email or WhatsApp with secure links. This automation scans your Excel sheet twice daily and updates the file to prevent duplicate notifications.
- Trigger: On a schedule (Scheduled · daily at 7 AM and 7 PM)
- Autonomy: Fully hands-off
- Expected setup effort: about an afternoon
- Tools/services involved:
  - Microsoft Excel 365: Reading payment records and updating status
  - Send Email: Sending personalized email reminders with links
  - WhatsApp Business Cloud: Sending formatted WhatsApp messages
  - Code: Filtering due dates and generating payment links

## Known pitfalls, handle each one explicitly in your implementation
1. WhatsApp Business Cloud has strict template approval requirements so pre-approve your reminder templates before deploying.
2. Excel row locking can cause conflicts if multiple instances run simultaneously, add a unique transaction ID to track updates.
3. Secure payment links must not be hardcoded in the template, generate them dynamically per user to prevent security leaks.

## Reference implementation
https://n8n.io/workflows/9844 (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-tour-payment-reminders/ via usecasesforagents.com