Mobile payments are booming. But are you missing out on credit card cash-back bonuses and rewards if you use your digital wallet?

You could be. On its rewards information website, American Express warns that cardholders may not receive rewards points in eligible categories if they use digital wallets like PayPal and Google Wallet. Other card issuers, such as Chase and Discover, sent out notifications to cardholders this spring that purchases made through mobile apps may not qualify for reward points if the technology is not set up to process the purchase in that reward category.