Problem using HC-12 graphical configuration utility, invalid responses
the 'SET' pin needs to be connected to ground to place (and keep) the HC-12 in setup mode. when this is done you should be able to click on the "check configuration" button and receive a popup response containing the device's current configuration.

if the popup response contains no configuration data then either the HC-12 is not in setup mode ('SET' pin not grounded), or the usb to serial bridge you are using is not working. check the bridge by disconnecting the HC-12 and shorting together TxD and RxD on the bridge. you can use any terminal emulator to check loopback is working.

feel free to join the backshed forums and ask further questions about the HC-12.

cheers,
robert rozee
(author of the HC-12 config utility)