Once the Launchkey MK4's firmware is up to date, open FL Studio and go to the MIDI Settings window:

FL Studio > Options > MIDI Settings

Here, make sure the Launchkey is set up as per the following steps:

1. 1. Select and enable the Launchkey MK4 MIDI and DAW input ports in the lower 'Input' section:
      
      • Launchkey MK4 MIDI
      • MIDIIN2 (Launchkey MK4 MIDI)
        
        
   2. Click on each Input port (MIDI and MIDIIN2) and set different port numbers for each port using the red 'Port' tab below.
      
      • Port numbers can be set to anything not already in use (except 0)
      • Choose different port numbers for the MIDI and DAW ports
        
        
   3. Select each input (MIDI and MIDIIN2) and assign the scripts for your Launchkey MK4:
      • Select the MIDI input, click on 'Controller type' drop down and choose 'Novation Launchkey MK4 MIDI':
        
      • Select the DAW input (MIDIIN2), click on 'Controller type' and choose 'Novation Launchkey MK4 DAW':
        
        • If you don't see the relevant option, try clicking 'Update MIDI Scripts' at the bottom of the window to ensure that FL Studio has been able to locate the latest version of the script.
   4. Click the output ports in the upper 'Output' section and set the Port numbers to match the MIDI and DAW (MIDIIN2) inputs. 
      • Launchkey MK4 MIDI:
        
      • MIDIOUT2 (Launchkey MK4 MIDI):
        
        

        The scripts you set in step 3 automatically link.
   

        5. Select the MIDIOUT2 (Launchkey MK4 MIDI) in the upper Output section and enable 'Send Master Sync'.

        6. Enable 'Pickup (takeover mode)' near the bottom left of the window.

        7. Click 'Refresh device list' in the bottom left corner.

   The settings should match the following:

If having issues, make sure you have installed the latest version of the Novation USB driver from the Launchkey MK4 Downloads page: downloads.novationmusic.com/novation

Once the Launchkey's firmware is up to date, open FL Studio and go to the MIDI Settings window:

FL Studio > Options > MIDI Settings 

Here, make sure the Launchkey MK4 is set up as per the following steps:

1. Select and enable the Launchkey MK4 MIDI and DAW input ports in the lower 'Input' section:
   
   • Launchkey MK4 MIDI Out
   • Launchkey MK4 DAW Out
     
     
2. Click on each Input port (MIDI and DAW) and set different port numbers for each port using the red 'Port' tab below.
   
   • Port numbers can be set to anything not already in use (except 0)
   • Choose different port numbers for the MIDI and DAW ports 
     
     
3. Select each input (MIDI and DAW) and assign the scripts for your Launchkey MK4:
   • Select the MIDI input, click on 'Controller type' and choose 'Novation Launchkey MK4 MIDI': 
     
   • Select the DAW input, click on 'Controller type' and choose 'Novation Launchkey MK4 DAW':
     
     
     • If you don't see the relevant option, try clicking 'Update MIDI Scripts' at the bottom of the window to ensure that FL Studio has been able to locate the latest version of the script.
4. Click the output ports in the upper 'Output' section and set the Port numbers to match the MIDI and DAW inputs. 
   • Launchkey MK4 MIDI In:
     
   • Launchkey MK4 DAW In:
     

     The scripts you set in step 3 automatically link.

     5. Select the Launchkey MK4 DAW In in the upper Output section and enable 'Send Master Sync'.

     6. Enable 'Pickup (takeover mode)' near the bottom left of the window.

     7. Click 'Refresh device list' in the bottom left corner.

The settings should match the following: