Make sure that the default admin$ share is enable on ServerName

Solution:

You need to add the 'admin$' share which is your C:\Windows location.

1. Go to C:\windows and right-click --> Properties
2. Hit advance sharing
3. Click the check box Share this folder
4. Enter the name admin$ and hit Permissions
5. I would recommend removing 'Everyone' and adding just the users that the PsExec command will use to execute.

Run the PsExec command again and this should resolve your issue.

Edit:

You can also turn on your AutoShareServer in the registry, which will automatically create the admin shares.

1. Start regisry regedit
2. Search for key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters\AutoShareServer
3. Change the AutoShareServer key to 1

You can also enable amins$ share by enabling File and Printer Sharing (SMB-In) Firewall Rule.

Go to Control Panel > System ans Security > Windows Defender Firewall > Advance Settings > Inbound Rules. Right click on File and Printer Sharing (SMB-In) from the list and select Enable Rule`. Normally, there are two File and Printer Sharing (SMB-In), one is for Domain profile and one is for Public & Private profile. I'm not sure which profile should be applied, Domain or Public or Private. For me, it's Domain profile.