Relock bootloader OnePlus Devices

Download the latest FW files from here

1. Install TWRP (OnePlus 5) and Magisk if you don't have them yet.
   
2. Magisk should allow you to slide "OEM unlocking" to "enabled" in developer settings (THIS IS IMPORTANT)
   
3. Reboot to fastboot (Refer to my older post if you do not know)
   
4. Flash stock recovery via fastboot. (Refer to my older post if you do not know)
   
5. Run locking via fastboot flashing lock command
   
6. Allow it to reboot and upon start up it will say device corrupted (THIS IS NORMAL)
   
7. Boot to recovery via the warning start screen.
   
8. Once in recovery, sideload latest FW.
   
9. Done & have profit.
   

Please comment if you face any issue or for any query.