Can I use a prepaid card to add money to Apple Cash card

Maybe (wish I could be more definitive). See the following from Add money to Apple Cash - Apple Support

After you set up Apple Cash1, you can add money to your balance using the debit or prepaid cards2 that you already use with Apple Pay in Wallet.

Footnote 2: You can't use credit cards with Apple Cash, and you might not be able to use some prepaid cards. You can't add money from a gift card, even if it's already in Wallet.