Look for Device unlocked: false and OEM unlock allowed: true . If the latter is false , go to Developer Options and enable "OEM Unlocking".
For those ready to take the "better" route, the process is straightforward but requires precision. It represents a rite of passage for a true OnePlus power user. please flash unlock token first oneplus better
Your phone will wipe all data and unlock. Look for Device unlocked: false and OEM unlock allowed: true