Hi, nnn946.
Welcome to the Apple Support Communities. We’re glad you decided to reach out about the issues you’re experiencing when attempting to reinstall macOS Sierra on your MacBook Pro.
You mentioned that you erased your MacBook, are you attempting to reinstall the macOS through Internet Recovery? You can tell if you’re in Internet Recovery when you see the spinning globe instead of the Apple logo at the beginning of the sequence.
This article explains:
How to reinstall macOS from macOS Recovery - Apple Support
If not, try restarting your MacBook Pro and starting up with the Shift-Option-⌘-R key sequence.
You will have to make sure that the date and time are set automatically in order for the macOS installation request to successfully reach Apple servers.
All our best.