Unlocking HTC desire 510 Boost phone to Freedompop network

I have a boost phone with the unlocking code and the sim card I want to use. When I turn on the phone with the new card it goes straight to the home screen. It says invalid sim card. I'm using a freedompop sim card. Unlocking code screen doesn't appears. The phone is not activate, but sim card is. What am i doing wrong and can anyone help?