LG G3 issue

My LG G3 is running on stock Android 6 Marshmallow, version V30b-EUR-XX, using custom recovery (TWRP), rooted.

The phone is network locked to my carrier. I got a network unlock code (NCK), however, when I enter the unlock menu (2945#*855#) and go to network unlock option, enter the code I get a "SIM network unlock request unsuccessful" error and the attempt counter does NOT go up (always staying on 1/10).

Note that I got my unlock code from the carrier, its valid. Then I went ahead a bought a key online from a website selling unlock keys. Got the same key as the one from carrier (wanted to confirm the key is indeed the correct one).

From that I concluded that the phone isn’t even trying to unlock the SIM.

Anyone got an idea on how to proceed?