Trying to get Windows Admin Center working on my home network I ran into a few errors

1. Trying to add the computer

A computer with the name 'pc1' was not automatically discovered. You can still add it to your connections list, but its availability cannot be verified.

2. Ignoring that and continuing, it still didn't want to work

Connecting to remote server pc1 failed with the following error message : WinRM cannot process the request. The following error with error code 0x8009030e occurred while using Negotiate authentication: A specified logon session does not exist. It may already have been terminated. This can occur if the provided credentials are not valid on the target server, or if the server identity could not be verified. If you trust the server identity, add the server name to the TrustedHosts list, and then retry the request. Use winrm.cmd to view or edit the TrustedHosts list. Note that computers in the TrustedHosts list might not be authenticated. For more information about how to edit the TrustedHosts list, run the following command: winrm help config. For more information, see the about_Remote_Troubleshooting Help topic.

After a bit of googling these are the steps from an elevated PowerShell session

Managing PC

Set-Item wsman:localhost\client\trustedhosts -Value pc1,pc2

where pc1, pc2 are the names of the remote PCs

Managed PC

Enable-PSRemoting -force
winrm quickconfig

With any luck, that is all you need to do.

Public / Private Network

If you get this error

WinRM firewall exception will not work since one of the network connection types on this machine is set to Public. Change the network connection type to either Domain or Private and try again.

Then find the name of the offending network

Get-NetConnectionProfile

and set it to private (if that makes sense security wise)

Set-NetConnectionProfile -name "Unidentified network" -NetworkCategory Private