I just got an order while I’m out of inventory???

I had been FBM but just switched to FBA two days ago and have a pallet being sent from my home to Amazon (scheduled pickup today). So when I switched to FBA my inventory went to zero obviously because my pallet hasn’t gotten to Amazon yet.

But this morning I got an order, and it is an FBA order. The pallet hasn’t even been picked up from my house yet. How were these ppl able to order? And what do I do?