Every sold-out variant leaks sales: shoppers see "Sold out" and leave. BackBy swaps Add to Cart for a "Notify me when back in stock" form on out-of-stock variants — one theme block, placed once, no code edits. Signups land in your waitlist grouped by product, with a live counter on your dashboard, ready to export as CSV and send through the email service you already use. BackBy never sends email for you and never reads orders or customer records. When stock returns, your list is ready.

• Sold-out variants show a notify-me signup form automatically — no theme code
• Collect-only: you keep your own email service, BackBy just builds the list
• Waitlist grouped by product, live capture counter, one-click CSV export
• Auto-flip: the form appears the moment any variant hits zero inventory
• Least-privilege: reads products only — no orders, no customer records