OnePlus phones (like the OnePlus 6, 7, 8, 9, 10, 11, etc.) are known for being developer-friendly, but they still require an official unlock token from OnePlus if the device is from certain regions (especially ) or if the bootloader is locked.
: Your device must already be carrier-unlocked (SIM-unlocked) by your provider. OEM Unlocking Settings > System > Developer options and enable OEM unlocking USB debugging : Unlocking the bootloader will factory reset your phone and erase all data. 2. Get Your Device Codes please flash unlock token first oneplus better