2 phones 1 only on wifi no SIM

[kotspot]

Just signed up for Spotify premium. I can log on with my iPhone SE no problem but when I try to login with an old iPhone 5C that I have hooked up to my stero which I was intending to stream from when at home it won't let me log in, I click on the login button and it doesn't take me to anywhere I can log in. This phone only runs on wifi and does not have a SIM card but it should work as an added device so why isn't it???