How can I fix the connection error ERR_CONNECTION_CLOSED?

This error can be caused for different reasons regarding your browser or internet connection. 

You might have to switch from WIFI to a cable connection or reset your router.

Use the following service to check if website is down just for you or for everyone: https://isitdownorjust.me/qrplanet.com/

You might try to access the website from a different browser, or you can delete the current browser cache and try again. Maybe you have a browser plugin that blocks the website.

Check if your antivirus or firewall software is blocking the website.

Execute netsh int ip reset, reset the Winsock interface netsh winsock reset and restart the computer

You might have to disconnect from your proxy or VPN connection and try again to connect.