How are you unlocking on DJI Fly? It was not clear at all to me how this could be done and at one point (I think when I tried the DJI website) I got a message that said I could not unlock on a mobile device.
You simply try to start the motors (for example by pushing both sticks down and inwards). If you are in an authorization zone, that should then bring up a prompt on the device screen where you have to self-certify that you are permitted to fly there. I believe the first time you do this, there is also a SMS code that gets texted to you from DJI that you need to also enter.
Once you complete that process, the zone unlocks. Your phone/tablet does need to have a data connection for this process to work, so if you are flying in a remote area without data, then you still would need to use the website authorization process ahead of time.
I've gone though this field unlock process dozens of times (both with DJI Go 4 and now DJI Fly for my Mavic Air 2), so I'm always a little puzzled why so many people think you need to use the DJI website for normal unlocking needs. I've almost never needed to do so.