(iOS 11) What does "ESN Locked," mean? (Sprint) I'm trying to sell my phone on eBay but they returned it and said the issue was that the ESN was locked. What does that mean and how can I fix it? The phone is connected to Sprint. 

Thank You!
In short, your phone is now near to impossible to repair. You cannot use it as a cellular phone anymore. It is deactivated, and the one thing you can do is sell it for parts. 

Sprint could have locked your ESN (Electronic Serial Number) because you did not pay your bill. Or if the phone was reported lost or stolen.