Connect the XBee coordinator to a laptop over USB and connect to the radio in Console Mode from XCTU to monitor the incoming packets.
Connect the Red wire of the USB cable you made to +, the White wire to L (Light), the Green wire to S (Switch), and the Black wire to -. The P terminal is reserved for the Photocell wire.
Place a magnet against the switch and power up Flora with either a battery or DC power. You should see the Green light on the XBee radio blink for 10 seconds then turn off. Before the XBee and Flora enter sleep mode, Flora will write out a message to the XBee to send to the coordinator to let you know its entering sleep mode. You will see the Red light on the radio light up when a message is sent or received.
When you remove the magnet, you should see the NeoPixel strip light up, a message that the Flora and XBee are exiting sleep mode, and that the mailbox lid is open. You will also see a mailbox closed message when the magnet closes the switch again.