Once again..... There is no reason to get another controller unless you WANT to use a phone or tablet.
Litchi works just fine on a
P4P+ controller installed through Amazon Appstore.
I'm living proof. I've been using Litchi on my + controller when it was first available to do so.
The USB cord MUST be attached to both ports before starting up the + controller.
It's the only way you'll get a pop up box asking you to choose either DJI or Litchi. Choose Litchi (tap just once, I like the option of choosing every time) you will get another query box asking you if you want to choose DJI again, choose cancel and you should have Litchi open, and if you've started your bird up, should be connected