Your customer, the buyer, is requested to pay Biller since Biller owns the payment collection process. It can happen that the buyer transferred the payment to you directly. In this situation, it's important that Biller is notified by either you or the buyer concerning this situation to ensure that we temporarily flag the payment request until further notice.
Together with the buyer, you can decide whether you will refund the Biller order in your Seller Portal and keep the payment or refund the received amount manually back to the buyer and ask the buyer to transfer to the payment to Biller instead. The buyer received our bank account details in the payment request.