When booking in with APC, you may notice that your postcodes are being updated by Shiptheory to be upper case. You may submit a postcode to Shiptheory as: bs4 3eh and Shiptheory will then update that on the label to BS4 3EH.
This is due to the fact that APC require upper case postcodes to be able to book in, so although it won't have any effect on your day to day operations, it's needed to ensure that APC continue to accept your shipments.
If you have any questions here, or are having APC shipment rejected for any reason you don't understand, please feel free to contact support.