I had plugged in the dongle to the USB port of the PC and open the MasterPlus+ software, why does it show “No Compatible Device Supported?”

To connect the MasterPlus+ software and update the CK721 firmware to the latest version, please toggle the switch on the side of CK721 to 2.4 GHz mode and make sure the dongle is plugged into the PC. The MasterPlus+ software will automatically read the current wireless firmware version of the keyboard, and pop out to tell you to update the firmware.

To fully update the keyboard, please switch the CK721 to WIRED mode with removing the dongle, plugging in the USB cable, and switching the side button to WIRED mode.

For detailed instructions, please visit here