You can find a full list of participating banks and credit unions live with Zelle here
If your recipient’s financial institution isn’t on the list, don’t worry! The list of participating financial institutions is always growing, and your recipient can still use Zelle by downloading the Zelle app for Android and iOS.
To enroll with the Zelle app, your recipient will enter their basic contact information, an email address and U.S. mobile number and a Visaor Mastercard debit card with a U.S.-based account (does not include U.S. territories). Zelle does not accept debit cards associated with international deposit accounts or any credit cards.