Can I pay another person if I only have the Apple Credit card in my wallet?
Can I send cash if I ONLY have my Apple Credit Card in my 'wallet"?
No - the Apple Card is a credit card. You would need to have funds in Apple Cash or have a debit card (or some prepaid cards to add money to Apple Cash) or send the money directly from a debit card.
See: Set up Apple Cash - Apple Support and Add money to Apple Cash - Apple Support and Send and receive money with Apple Pay - Apple Support