When connecting to a PS-Session using a IP address it adds some requirements, You must either have the remote device configured to use ssl or have the IP address listed in your trusted hosts.
The solution is to either try use the host name for the device, I have had great success with this. Or play with the trusted hosts list. In my experience it works consistently if you add trusted list entries on your machine and the remote machine as well. You can also specify:
Set-Item WSMan:\localhost\Client\TrustedHosts -Value "*"
This will basically set all machines to be in the trusted hosts list, It has its cons like all machines being trusted but in certain restricted networks its acceptable. Doing this on the host and client machine seems to yield best results.
When specifying -Credentials
it expects a credential object, You can craft one before the cmdlet to avoid entering it every time like so:
$secpass = convertto-securestring "Password Here" -asplaintext -force
$cred = new-object -typename System.Management.Automation.PSCredential -argumentlist "Username Here", $secpass
Enter-PSSession -ComputerName "<container ip>" -Credential $cred
Coding credentials like this in a script is bad practice, You should look in to storing credentials in scripts properly, there are plenty of good resources on it.