Refund failed due to insufficient funds in your Paypal account (refund customer)

Hello, I am new to this situation. A customer brought an item off me but the item was unavailable to ship. I removed the active product from my store and then trying to refund the customer. However I get this error that’s preventing me. I have updated my payment option and I still get this error. I really want to refund this customer as soon as possible.

I probably learnt not to delete the product or else the refund page won’t register what to refund.