1. Windows - "Controller Not Connected" message

If you get this message on the MP Host software plugin, first, ensure you have disabled the MIDI and OUT of C1-xMP1 in the DAW as instructed here

If another app is using the C1-xMP1 then it will not be available for the MP Host plugin to use it.

Connect and check procedure:

1. Connect the USB cable provided directly to the computer USB-A port (not USB-C) from the USB-C MIDI port on the controller.

The MIDI port works independently from the other ports of the controller - Display & HDMI -  so it does not matter if these are connected or not.

2. Go to Device Manager and check that the C1-xMP1 shows up

Also check that the device is enabled in the device manager. (right click on C1-xMP1)

If it does not show up in the device manager, there is a connection issue and you may try a different USB-A to USB-C DATA cable or connect directly to the computer instead of through a USB hub or KVM switch. 

Connect the cable provided directly from the MIDI port of the controller, to the computer’s USB A port (not USB-C port).

If you are connecting to a USB-A port directly to the PC and it still does not show up in the device manager, check this article

3. If the C1-xMP1 does show up in the device manager then check that you have completely disabled the MIDI IN/OUT of C1-xMP1 in the DAW, as instructed here. 

All midi drivers on Windows are exclusive, meaning only one application can use them at any time. In Windows only one application can use a MIDI device. On the Mac MIDI devices can be shared in between applications. 

If the controller is active (IN/OUT) in the DAW, disable and restart the DAW, then load the MP Host again. The problem should be fixed.

If it is disabled in the DAW, check that the C1-xMP1 is available and no other application is using it. You can use a free app like Midi View to check.