Why do I need to deactivate my SIM card when I'm not using it, and how do I do this?

You'll be charged for using the 3G SIM at a rate of up to £10 a month, depending on how many days your SIM card is active - so if you're not using it, it's a good idea to deactivate it. You can do this on the device or on your Clover Dashboard. Just find the Wireless Manager app and locate the SIM card (if you have multiple devices there will be more than 1), you can check the S/N (Serial Number) of the SIM card by opening up the back of the machine and taking the SIM card out. Then select De-activate on the one you wish to stop billing.