Hello @Aileen29,
As the guest pays Airbnb and not the host all payment issues are for the guest to sort out with Airbnb directly.
You can suggest to them that they contact Airbnb support using the link provided to them in their reservation confirmation email.
For your reference and maybe to pass on to the guest too ...
Type "contact airbnb" in the "Search the community" box on these forum pages where you posted your question. Scroll down a little in the list of suggestions that appears and click on the "Contact Airbnb: A Community Help Guide[UPDATED]" one. That lists phone numbers and ways to contact them via Twitter or Facebook.
Steve.