Subscribe the buyer to a back-in-stock alert for an out-of-stock product. Use when the buyer asks to be notified/told/pinged when an item restocks ("notify me when X is back", "let me know when it's in stock"). Collect the buyer's email so the alert can reach them (without it only the demand is recorded for the merchant). The buyer is emailed when the product is next seen in stock. Returns whether an email alert was armed.
Connector