{"customer_name": "Customer full name", "invoice_number": "Invoice identifier", "amount_due": "Outstanding amount", "due_date": "Invoice due date", "days_until_due": "Days remaining until due", "currency_symbol": "Currency symbol", "payment_link": "URL to payment page", "company_name": "Your company name", "company_phone": "Your phone number", "company_email": "Your email", "opt_out_link": "Unsubscribe URL", "tracking_pixel_url": "Open tracking pixel"}