it is a registration error that comes up when your carrier's network fails to authenticate your user credentials. you need to contact Sprint to clear it.
I'd like to recommend creating a account so me or other members can assist you, as guest have limitations in replying here and if we need further Information to communicate with you.
I'll provide a link to register, please come back to your post so we can further assist you . Thank you
Welcome to Android Central! Do you have the Galaxy S5 or the Note5? They're not the same. Also, did you get this phone from Sprint, and are you currently using it on Sprint? Or did you bring it to a different carrier?