Contact their customer service, and they should be able to help you with that. They respond quickly, and they are are pretty straight forward.
Coinbase is a Cryptocurrency Brokerage platform. They are not a coin exchange, they basically connect buyers with sellers, and charge a fee for the transaction. They are showing you the best prices from other exchanges, and allowing you to buy at those prices.
I use Binance, because the customer service and information are outstanding, and the interface is simply and straight to the point. I do all of my transactions on there, with Coinbase being my feed account.