We hadn't charged a single live customer yet, but we had done plenty of tests using the Stripe testing environment. So we go live with a huge launch event, and we have customers signing up in droves. When they get to the last step -- payment -- they get an error.
Logging in to the dashboard I didn't see any indication that there was anything wrong with our account. No alerts or notices. We had already gone through the approval process you go through when signing up, and been told we were approved.
The thing that surprised me the most was that there was just no indication anywhere that our account would not be able to charge cards. Wouldn't it make sense for there to be an indicator somewhere that just says "Not ready yet"?
Apparently, they had never even begun reviewing/vetting us since the time we signed up for the account months earlier. We reached out to customer support and it took them about two weeks to get us activated. And, similar to OP, they never gave us a shred of information about what was going on. I still don't know to this day what the issue was.
Next time I build something with Stripe I'm going to test it in production before launching, with my own real credit card!