In the script editor, in the Paste action you have in step 4, click on the target object, currently "ses[0]" in your script. It should look like this:
The arrow at the right-hand end is the object picker. Click on that and you can then select the screen element you want to paste the value into. In XK03 I'd expect that to be "ses[0]/wnd[0]/usrUSRAREA/ctxtRF02KLIFNR".
Steve.