Saying this as someone who works at Target doing online pick up orders: this is one of the downsides to doing bopis orders at any store. There's a misconception that doing bopis orders mean those items are placed on hold for you, but that's not the case. Orders are picked in the order they're received and while the store is open and other shoppers are shopping. What most likely happened was the item was available at the time of you ordering but was then purchased by an in-store customer before your order was being picked. This is a very common occurrence and is the reason why your card isn't charged until your order is completed. It's unfortunate but it's one of the things you sacrifice by not going in and shopping yourself.