I have a problem. I have to cancel a guest's stay in the apartment. I found out a few hours ago, that we have a sewage spill in the apartment and water can not be restored. I cannot fix this by the time the guest arrives. I cannot cancel as airbnb website gives an error: Unable to perform action. Please try again through the website or contact support if you need immediate assistance. I have tried multiple times. There are 13 hours left until guest arrives, though in fact the guest arrives in more than 24 hours.
You should contact Airbnb customer support immediately and tell them of the problem.
Phone numbers and other ways to contact them can be found in the "Contact Airbnb: A Community help guide" post that will appear in the list when you type "contact airbnb" in the "Search the community" box on these web pages where you posted this question.
You can cancel under Extentuating Circumstances - look up details on Airbnb Help Centre.
As Steve said, if you don't have contact details - look at the first post in the Community Help forum all the phone numbers are there. Call them now and contact your guest ASAP so they can make alternative arrangements.