Sim unlock Galaxy Grand Prime

hi all i just got a Galaxy Grand Prime from t-mobile i want to sim unlock it and i know there are websites who can sim unlock if for like bucks but all of the sites say them same thing if your device does not prompt you for unlock , or you using a Remote Unlocking APP the unlock will not work so my question is there a work around the to remote app because t-moible has the app in the phone and i want to unlock it for international use.