unlock a paid off OnePlus Nord N10

Hello, I have a OnePlus Nord N10 I paid off a few months ago. I was planning to give it to a friend, but when I go through the device unlock feature in the app and the devices Settings it still says it's Locked to the carrier. It was paid off completely from my account in April or May. I upgraded to a OnePlus 10T months earlier in November last year. So I just paid off the rest of the balance recently. But I can unlock the phone. If the phone is completely paid off why can't I unlock it? Isn't the main requirement to pay off the balance? What is the reason they won't unlock the phone?