Since this formula's own guarantee is calculated from your purchase date, your order confirmation email is worth keeping accessible from day one.
Your order number, the purchase date, the exact package and price you paid, and any correspondence with customer support — all worth keeping in one place, not just your inbox.
Since this formula's own materials describe contacting support for full guidance rather than an automated refund, having your order details documented and ready speeds up that conversation within the 60-day window.