All Best Buy ip x’s Amongst others are subject to the US Reseller Flex Policy and will follow the carrier lock policy of whichever carrier's SIM card is used to initially activate the device.
I’m requesting a carrier unlock code for an iPhone X that was lent to us to use for acouple months but wasn’t purchased through any carrier but it was unlocked when we were allowed borrow it but appreciate when the Tmobile sim was inserted I auto locked the phone. We have to give it back to the owner now and he needs it unlocked.
The original owner has to jump through hoops now to get it unlocked. It's a Policy Apple should do away with. Carriers do not know it's theirs because Apple never gives them the IMEI's to let them know. Since it's not in their system T-Mobile has to wait to hear from the right people on Apple end to start the process.