I don’t know who put the lock there - phone maker ? phone seller ? provider of 1st SIM card ? provider of 2nd SIM card ? other ? I just know that ONLY my current SIM card (the 2nd) works in my phone. No other SIM card will work in it.
I don’t know the correct procedure to remove the lock without bricking the phone. Or, how to unbrick it, if I do.
Perhaps I am being too cautious, but some of what I have seen online seems a little dubious, and I’m not sure I can trust myself to distinguish between good info and bad.
You are one of the few who have actually unlocked a dumb phone in real time.
Could I be so bold as to ask if you would be willing to give some of your time to find a good tutorial with unlock codes for a Samsung GT-E3210 dumb phone made about 2013 ?