I have similar problem.
First of all guest sent me a message in Airbnb inbox asking about availability for the certain date. Then I Pre-approved his reservation and waited for him to decide will he confirm his arrival to Split. After that, tomorrow morning he tried to finalize the booking but he could not. So he asked me to hold the reservation for him until he come back from work. I did that. Finally, he returned from work and tried several times to pay the reservation but Airbnb sent him this error message:
''Unfortunately, a server error prevented your request from being completed. Airbnb may be undergoing maintenance or your connection may have timed out. Please try again.''
So he tried few more times but without success.
I hope that someone can help me.
Thanks,
Oriana