[AC Question]

I have a fully paid for Galaxy S6. It is eligible to be unlocked and I have the codes. However, when I put a foreign SIM card in, I am not asked for the unlock code. It just says "Invalid SIM card: Network locked SIM card inserted". I cannot get it to give me a field to put the unlock code in. I can't use T-mobile's device unlock app because I'm out of the U.S. and not on T-mobiles network. Any thoughts on how to get access to the prompt to enter my code? Nothing seems to work.