The network you use at work or school may have a firewall or a proxy in place for security reasons. A side effect of this is that you have limited access to Codecademy. You will be able to visit Codecademy but not everything works properly. You may also run into this if you are using Wi-Fi in places like cafes and libraries. If you find that you have no trouble accessing Codecademy from home but when you are away you find the lessons won't load or submit as expected then this could be the problem.
If you're at work or school, ask the tech support team to see whether firewall settings are restricting your access to Codecademy. Let them know that we use port 80.
It is possible that your own home network has been locked down to improve your network's security. If that is the case, and depending on if this was done by you or is part of your family's parental control settings, this will be something that you or your parents can correct.
These are the necessary URLs that will need to be whitelisted for Codecademy to fully work:
www.codecademy.com external-production.codecademy.com cdn-production.codecademy.com terminal.com herokuapp.com cdn.mxpnl.com