I think this is because the verification payment has failed. Odd thing is that Airbnb are the only people who know this and don't contact the prospective guest at all to tell them about payment problems
As a host I was on the receiving end. Payment was stuck in pending on the guest side and at "Awaiting Verification" I went through Airbnb help (chat) and they told me that guest payment was failing (they had'nt told the person who's pay't was failing though), and suggested I passed the message on (Which I did ).
Further they told me the only way to sort the problem was for guest to cancel request and create a new reservation / booking request.
Sadly, probably due to embarrassment they cancelled the request and I didn't hear from them again.
Why couldnt airbnb have told the guest of the issue right at the start and he could have corrected it right at the start?
Seems like there is a hole in the process to me