His error happens when you're trying to connect to a friend's PC and they haven't accepted your request to connect.
Your friend can accept your connection by either clicking accept in the host tab of their Parsec app or pressing CTRL + F1 when the notification appears.
If the host doesn't get a pop up notification from Windows, they probably have notifications disabled or on quiet hours. They should check their host tab of their Parsec app instead.
My friend didn't receive a notification in Windows or in the Parsec host tab?
You both need to restart your Parsec application - if you're on Windows, this means right clicking the Parsec icon in the task tray and clicking Restart Parsec.
On Mac/Linux/Raspberry Pi/Android you should just quit the app and re-open.
If that didn't work, there may be something weird going on with your internet connection or installation of Parsec.
You can diagnose further by seeing if you, the client, can connect to other hosts without the same issue, or the host, can let other people connect OK.
Once you have that information, join our Discord and let us know what is going on.