You are able to attempt the Law (LW) paper before you have finished the Applied Knowledge papers, but in order to do so you must enter (and pay for) any of the Applied Knowledge papers that you have not successfully attempted
So, using the previous terminology, you may enter for F4 but you will need to enter also for F3 in the same session
This doesn’t mean that you have to attend the examination centre and actually attempt F3. It means only that you have to enter for the exam and pay the entry fee