Reloadable cards unfortunately aren't available for the Instant Deposit feature. They need to have a linked bank behind the card.

From the Instant Deposit Unavailable Troubleshooting Help Page:

We currently support most U.S.-issued Visa or MasterCard debit cards. Credit cards, ATM, PayPal, or prepaid bank cards aren’t supported at this time. You’ll need to link a supported debit card and bank account to your Square account to use Instant Deposit.

We use a variety of card networks to send funds. For every debit card, both the card network and bank must be set up to receive funds instantly. Unfortunately, we can’t confirm if a card is supported until an attempt to link it to Square has been made.