I am now having this exact same issue, except I'm having it while trying to pay for a booking up front.
I'm trying to book a 31-day stay, paid up front. My bank says the money is available. AirBnB is telling me that my payment is being declined, and specifically declined by my bank.
The issue is clearly on AirBnB's end. Not only are they saying that my bank is the one declining while my bank says the funds are available, but after the decline they sent me an official notification stating (redacted for privacy, emphasis mine):
"Action required. Your payment failed. Please pay [amount] by Jan 2 to keep your [location] reservation."
It's currently May. I'm trying to book for May through June. Yet they want me to pay "by Jan 2." It's clear that something on their end is borked, yet they refuse to admit it. They keep saying that the issue is on my bank's end, and whenever I ask about the incorrect dates they're sending me in notifications they ignore the query. (Notably, they don't claim it's a nonissue or that it's not indicative of broader problems. They just don't acknowledge it at all.)
It should be noted that the host has been as helpful as humanly possible, and has even agreed to take the listing down for a few days so it doesn't get sniped while I try to address this issue. That's above and beyond, as far as I'm concerned - so massive respect for the host. It's just that AirBnB themselves are not being helpful about this.