You are helping me build the following AI agent workflow.

## Goal
Promo Code Expiry Alert System: Promo codes expiring soon? Get urgent alerts via email and Slack while tracking all details in a shared sheet.

## Specification
- What it does: Stop worrying about expiring promo codes; this workflow automatically monitors their deadlines and sends you urgent reminders via email and Slack before they lapse. It keeps your team aligned by calculating remaining days, categorizing urgency levels, and logging all tracking details in a shared Google Sheet so nothing slips through the cracks.
- Trigger: Triggered by an event (Event · on webhook POST request)
- Autonomy: Fully hands-off
- Expected setup effort: about an afternoon
- Tools/services involved:
  - n8n: Workflow orchestration and automation logic
  - Webhook: Receiving promo data from external systems
  - Google Sheets: Storing and tracking promo code details
  - Gmail: Sending email notifications for expiring codes
  - Slack: Posting urgency-based alerts to team channels

## Known pitfalls, handle each one explicitly in your implementation
1. Timezone mismatches can cause incorrect urgency calculations so always normalize dates to UTC before processing.
2. Gmail API quotas may be exceeded during bulk alerts so implement a small delay between email sends.
3. Slack message formatting breaks if special characters are not escaped properly so sanitize all input strings.

## Reference implementation
https://n8n.io/workflows/15238 (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/promo-code-expiry-alert-system/ via usecasesforagents.com