I connected a PayPal account but I still can not pay someone back?

If you want to pay someone back that person needs to have a PayPal account connected as well.  You can ask a person to connect a PayPal account in order to pay someone back.
Be aware you also need to have a payment method (e.g bank account, credit card) connected to your PayPal account. Go to your PayPal account to add a payment method.