Crypto companies are turning to a tried-and-true trick from the banking world to entice new users, but with a major curveball.

Coinbase is joining the rush to offer a credit card promising crypto rewards, with cardholders able to earn up to 4% back in bitcoin for everyday purchases. Applying for the card, available this fall, will require a subscription to Coinbase’s premium crypto-trading service.

High-profile crypto companies, including the Winklevoss twins’ crypto exchange Gemini and Crypto.com, have announced similar offerings. The rewards would be paid through customer accounts on the exchanges.

Unlike with cards that offer cash back, the value of crypto rewards can rise and fall sharply given the volatility of the digital currencies. That extra layer of risk comes on top of the usual credit-card pitfalls, such as high interest rates and debt accrual.

The risk—and potential for gains—is part of the draw for some users.