Just to clear this out to you, awaiting payment is always caused by the guest's bank. When guests book, Airbnb's system will verify if the payment method is valid, once verified, then this is only time it will charge a payment. This is where the problem with bank's system comes in, although the bank's system allowed Airbnb to verify the payment method, it not allow Airbnb to charge payment. The guest has to sort this one out with their bank because Airbnb does not have access to bank accounts or the bank's system to fix this. This is a common issue vendors like Airbnb encounter due to banks ever tightening security system. Oftentimes, this can be resolved by guest quickly, if they would cooperate. So I suggest to give the guest 1-3 hours to do so, especially if the reservation would be in a week or so still. If you feel that you have given enough time for the guest but has not resolved it, you can always contact the guest first, and ask them to withdraw, or contact Airbnb to withdraw the request of the guest and free up your calendar.
Awaiting verification is also not entirely the fault of Airbnb. All guest right now are being required to submit a photo ID, even hosts are, and there are a lot of users who are not complying with this. So when they will book, the system will ask them to submit a photo ID, and their reservation status will become awaiting verification. Check your account, maybe you are one those who have not submitted a photo ID yet.