The ATWINC1500 module must be upgraded to firmware version 19.3 for the application to work.
The firmware upgrade process consists of first programming a serial bridge application to the megaAVR on the Xplained Mini board. This will then act as an interface between the virtual com port and the ATWINC1500 module and transfer the firmware from the computer to the ATWINC1500.
To do this, make sure that the Xplained Mini is connected to the computer with the USB cable, and that the ATWINC1500 is connected to the pin headers on the right side of the board. By running the .bat script found in the WINC1500_FW_UPDATE folder in the .zip file accompanying this application note, the serial bridge will be programmed to the megaAVR and the new firmware will be transferred to the ATWINC1500. For the ATmega328P, the script to run is "mega328p_xplained_mini_firmware_update.bat". Update scripts for other Xplained boards are also included in this folder.