In my case, I got the phone new in one country, where I used the 1st SIM card I put into it. I wasn’t aware of any requirement to use any particular SIM card, or to use it for any particular time.
Some time later I was in another country. I wanted to put my 2nd SIM card in, but the phone wouldn’t accept it.
I took it to a phone shop and had it unlocked.
I have been using this 2nd SIM card for years. This SIM card is in no way connected to the phone seller or phone maker, and it is from a different country.
BUT now I find that this 2nd SIM card is the ONLY SIM card the phone will accept.
How do you interpret this data ?
How would this lock be activated on an unlocked phone ?