Lg g3 d856 topic

Plz guys :(
I have lg g3 d856 dual sim ... I have tried to root it by purple drake and ioroot but i have a problem in stock recovery when i click on apply update from external sdcard to make root this problem face me ....
E: signature verification failed
Installation aborted

plzz i want solution for that :(

Sorry i can't share pics because iam a new user :/