You may need to know you device mode first.
Red button of NEJE 1/2/2S Series device:
In GRBL Mode, short press red button is disabled.
In IDLE mode, press once will enter NEJE mode and start homing, after homing, device will stay in NEJE mode.
In NEJE mode, when device is waiting(after homing success state), Press red button once will start preview, press again will start working progress, the work content is your last work content, press once will pause the work progress.
For some firmware, long press(about 1 second) the red button will turn off your device(even in GRBL mode), in power off mode, your device red led will keep off, and the connection of computer will lose, so, you can’t connect to your device at power off mode.
Red button of NEJE 3 Series device:
Short press the red button will pause the work progress at NEJE mode and GRBL mode, you can use this button as emergency stop button, but you can’t resume the progress by press the red button at GRBL mode, you need resume at control software.
Long press(about 1 second) the red button will change mode. GRBL->NEJE->GRBL->NEJE cycle
Long press(about 3 second) the red button will turn off your device, long press the red button again will turn on your device.