How to unlock metro pcs samsung core prime with code...

[AC Question]

I got my unlock code today, put my unsupported T-Mobile sim card in, and waited for an unlocking option to show up like all YouTube videos show. Nothing happens. A black screen shows up that says Network Lock: [insert long passage here]. I click OK and it takes me to my home screen. Nothing shows up so I can input my code and I have no idea what to do because it seems like no one has this problem. PLEASE, I'm in dire need of HELP! Thank you.