That is Hardware Issues.Apple with the IOS update makes that to activate the iPhone IMEI,Serial,WI-FI,Bluetooth needs to be match.So,on old IOS that problem is shown as error -1 now shows Unable to active.This fault was not solve by software that is the hardware related faults.
The baseband data is not present on the phone that the phone don`t have IMEI number check it out first.On the other hand if the fault was from BBCPU that can`t be solved but if it was from BBpmu that can be fixed.It needs hardware skills.If you have hardware skills that [https://www.youtube.com/watch?v=d989PEe5XXg&t=184s|videos] makes to solve that issues.