Sim not supported

I bought a phone from someone it was a sprint phone but told me he used it through Verizon well I bought a byod from straight talk and it still pops up sim not supported.. well I put a straight talk SIM card in and tells me sim not supported well when I take it out I got to my about phone it says my carrier is tfw 35.0 I tried a Verizon sim said sim not supported I take it out go to my about phone and it says Verizon.. what is going on?