I do the following process which has worked for me:
(1) On a PC, I go to https://fly-safe.dji.com/unlock/unlock-request/listUnlock - DJI FlySafe, and make sure I’m logged in with my DJI account. Then I select “New Unlock Request” and follow the instructions. Basically you select a zone you want to unlock, enter your drone info, pilot info, reason for flying and the date you want to fly. Authorization seems to be automatic, and you are presented with a list of authorizations, with the new one on top.
(2) I then connect my drone to the RC and open the DJI Fly app. I hit the < icon in the upper left corner until I see “Profile” on the bottom of the screen, select it, and scroll down the right side of the screen until I see “Settings”. I select Settings, then scroll down the left side of the screen and select "Unlock GEO Zone. You should see the authorization you created in step one. Hit “Import to Aircraft”.
(3) Hit the < icon (upper left of screen) until you see “Go Fly”. I make a test hover at this point in DJI Fly.
(4) I then close DJI Fly and open Litchi and make a test hover to verify I’m good to go.
Hope this helps. I have used this on my iPhone and my son has used this on Android.