I bought a sprint sim free iphone 6 model A1586 brand new, and was trying to activate it with my metro pcs sim card in it and got error message saying sim not valid, I tryed other sim card nd got the same message. Can someone tell me what the problem

Ok so I bought a sprint sim free 16gb iphone 6 model A1586 brand new, I try activating the phone with my metro pcs sim card and got error saying sim not valid the sim insinde this phone is from a carrier that is not supported in the activation policy etc.. So I tryed several other sim card and still got the same error message, so can someone please help me and tell me what the issue may be bcuz I really wanna use this phone nd I hate to waste my hard earned money.. I even purchased a straight talk sim kit for $60 which included sims for at&t, T-Mobile, Verizon, sprint, nd a network access code card. Now all Sims are nano nd micro nd the kit is GSM & CDMA compatible. I tryed all the nano sim cards tht came with the kit and I still got the same error message "sim not valid” but when I look on apple website to see what mobile network my model iphone is compatible with it said straight talk will work bcuz it uses same network as model A1522 nd A1549. So PLEASE PLEASE!!! Someone help me figure this.