There could be payment issues like not sufficient funds on the card. I would be very wary regarding this extension to the stay - keep airbnb emergency number at hand.
@Nathan44 perhaps you have "one day advance notice" checked in the platform? You can bypass by clicking the reservation, "report a problem" to visit resolution center, then simply sending the guest the fee request for additional services to extend the stay. That works for all miscellaneous fees. As soon as the guest accepts, the payment is confirmed and sent.