If a person preapproved a payment it does not mean that he already made a payment. It only means that he allows Zaxaa to take a funds from his PayPal account. But if from the first payment the payment fail (i.e: because of not enough funds) then Zaxaa will not record it and will never take any payments again from this preapproved payment.
If you see error: The payment can not be processed because no payment source is available
It's likely that your paypal account is not properly configured to fall back on the credit card if the PayPal balance isn't sufficient to cover the transaction. It may be that the credit card is not properly entered or isn't "verified".