If you are unable to bring up the item by scanning the barcode or typing it in, it could be because there is a blank space character at the end of the barcode in the temporary item's record.
1. Go to the patron's Holds tab and click on the barcode that appears next to the item's title.
2. Click Edit Item.
3. Click inside the Barcode field and remove the space at the end of the barcode.
4. Click Save Edits.
5. You should be able to check out the item as expected.