Phase 1: ~100 products    — Validate format and field correctness
Phase 2: ~1,000 products  — Validate batch processing and chunking
Phase 3: ~10,000 products — Validate performance and stability
Phase 4: Full catalog      — Production launch

{
  "id": "prod_001",
  "variants": [
    {
      "id": "var_001_black",
      "title": "Wireless Earbuds - Black"
    }
  ]
}

{
  "price": {
    "amount": 9999,
    "currency": "USD"
  }
}

Validation checklist:
1. URL format is valid (starts with https://)
2. Special characters are properly encoded (spaces use %20)
3. URL is publicly accessible (no login required)
4. No expiring session parameters are included
5. Image URLs return valid images
6. The utm_medium=feed tracking parameter is present

Test steps:
1. Connect to the SFTP server using the provided credentials
2. Upload a small file to verify write permissions
3. Confirm the file arrives in the target directory
4. Verify the file size matches (transfer integrity)
5. Attempt to overwrite the same filename to verify the overwrite mechanism

GET /product_feeds/feed_abc123
Authorization: Bearer api_key_123
API-Version: 2025-09-12
Accept-Language: en-US
User-Agent: MyStore/1.0
Timestamp: 2026-04-11T08:30:00Z

POST /checkout_sessions
Content-Type: application/json

{
  "line_items": [
    {
      "product_id": "prod_001",
      "variant_id": "var_001_black",
      "quantity": 1
    }
  ]
}

POST /checkout_sessions/:id
Content-Type: application/json

{
  "shipping_address": {
    "line1": "123 Main St",
    "city": "San Francisco",
    "state": "CA",
    "postal_code": "94102",
    "country": "US"
  }
}

POST /checkout_sessions/:id/complete

POST /checkout_sessions/:id/cancel