Question about In-stock Head Start

Hello,

I received an email from Amazon saying that “I have received a customer orders through In-Stock Head Start, but don’t have enough inventory that’s on the way to fulfillment centers to complete the orders”

I am confused why Amazon let a customer order from my account when there’s no shipment for that product that is on its way to the fulfillment center. Also, What happens if I don’t supply further inventory for this item? Will it affect my IPI score or my Account Health? Thank you.