When using the POS, any abandoned order as well as any orders that experience an error when checking out will be sent over to in_checkout status. This is a hidden status that will hold both POS and Direct Website orders.
DISCLAIMER: Direct Website orders that are in in_checkout status will not hold any quantity on the order, meaning they will not have any affect on your inventory. Please leave them as-is, and only attempt to manipulate the POS orders that are shown in this status.
Here is the link for the in_checkout orders section of your admin:
(replace the x's with your database name, just like what is displayed in the website URL when visiting your admin.)
You are presented with a list of your In_Checkout orders:
From here, you can view all of the orders that were abandoned by customers or experienced an error during checkout.
Note: If you apply an additional search filter here, the display will revert to not show In_Checkout orders
Reference this list when you are searching for a POS order that had an error during checkout. After you locate the order, you can then move it out of In_Checkout into any other status you wish and then process the order in the admin. This is especially helpful if the order was too large and will not complete in the POS. The benefit of saving these orders is that the quantity has already been removed from your inventory and you will not need to fix it after the fact or rebuild the order.