Send by Flutterwave, a money-transfer service, is rolling out a physical naira card for Nigerians living abroad who are visiting the country over the holidays. The card is linked to the app and can be topped up with U.S., European or U.K. bank cards. It works on POS terminals, ATMs and contactless payment systems across Nigeria. The product is designed to help visitors bypass cash-withdrawal limits, unstable exchange rates and frequent problems with foreign cards.