How to unlock an Iphone

I paid off my iPhone X today to give to my niece who has t mobile. I went to unlock the device with the link i was given through at&t but when i put in the imei code I’m given the message saying that that imei isn’t connected to an at&t phone, when it is. I’m currently at a loss as for what to do. Any help would be appreciated. 

i need help,Iwant to unlock my device

The first step is to make sure your device is eligible to be unlocked: https://www.att.com/esupport/article.html#!/wireless/KM1262649?gsi=4nzdeu

Then you just submit your request: https://www.att.com/deviceunlock/#/

Once your unlock request is confirmed, you should be able to put in the new SIM card and be good to go. I've seen some users need to backup and restore from backup for the unlock to go through

I want to unlock my iphone

My equipment was reported lost. This is the equipment sent by my friends and friends when I went abroad. It cannot be used normally after returning home. The inquiry was reported lost. I want to ask what should I do. I want to unlock my equipment and provide IMEI

If the phone was reported lost or stolen, it cannot be unlocked.

If your friends sent you the phone, you should probably take it up with them why it's reported as lost/stolen.

I contacted my friend and did not report it. Maybe someone else maliciously reported it missing or you can inquire about what is wrong with my contract. I can provide the phone number and IMEI code. I don't know whether these two numbers are matched. I really want to solve my problem through the official. Do you have any good suggestions

If you want to handle this through official channels, you'll need to contact AT&T Support, most likely through chat.

I hope you get everything figured out

thankyou