PayPal Holdings Inc. /zigman2/quotes/208054269/composite PYPL +0.93% said late Wednesday it has agreed to buy Honey Science Corp., a platform for shopping and rewards, for about $4 billion. Honey "will transform the shopping experience for PayPal's consumers while increasing sales and customer engagement for its merchants," the company said in a statement. Founded in 2012, Honey tracks prices and alerts and manages rewards programs, and PayPal said it has about 17 million monthly active users and works across about 30,000 online retailers. The deal is "amongst the most transformative acquisition in PayPal's history," the company said. The transaction is expected to close in the first quarter of 2020. PayPal said it expects it to add to PayPal's adjusted per-share earnings by 2021. Shares of PayPal fell 1.2% in the extended session after ending the regular trading day down 0.8%.