There could be a glitch in Etsy's system. Or while the buyer have received confirmation that they have placed an order, the $$sale amount itself has not yet been approved by Etsy's payment Processor.
The most you can do is message them back, saying you do not have access to any of their payment info.
Advise them you will contact them on a specific date - say Monday, 6th - if you have not received notification from Etsy that the listing has sold.
The buyer will then need to be the one to contact Etsy to get everything straightened out - there isn't anything you can do.
Hopefully the sale goes thru for you with no further bumps in the road.
