I was trying to sim unlock bad IMEI (financed) all services refused to unlock I managed to sim unlock very easy
1 you need to convert to international version follow this thread By AnonymousTipster ( great thanks ) (https://xdaforums.com/oneplus-6t/how-to/t-mobile-6t-to-international-t3888307 )
2 unlock bootloader
3 type this commands
adb reboot bootloader
fastboot erase modemst1
fastboot erase modemst2
fastboot reboot
thats all
you can also backup modemst1 and modemst2...
Read more
1 you need to convert to international version follow this thread By AnonymousTipster ( great thanks ) (https://xdaforums.com/oneplus-6t/how-to/t-mobile-6t-to-international-t3888307 )
2 unlock bootloader
3 type this commands
adb reboot bootloader
fastboot erase modemst1
fastboot erase modemst2
fastboot reboot
thats all
you can also backup modemst1 and modemst2...
Read more