Custom PowerShell command for batch edit not working

Greetings, all!

We need to update a large quantity of entries (connections) to now use an SSH Gateway. We exported an XML of a connection that is already set up how we want:

  <ConnectionHandbookPages />
  <Connections>
    <Connection>
      <ConnectionType>SSHShell</ConnectionType>
      <CredentialConnectionSavedPath>Creds\xxxxxxxx</CredentialConnectionSavedPath>
      <Group>xxxxx\xxxxxx</Group>
      <ID>xxxxxxxxxxxxxxxxxxxxx</ID>
      <Name>xxxxxxxxx</Name>
      <OpenEmbedded>true</OpenEmbedded>
      <Stamp>xxxxxxxxxxxxxxxxxx</Stamp>
      <Terminal>
        <EnableLogging>true</EnableLogging>
        <Host>xxxxxxxx</Host>
        <LogFilename>$NAME$-$DATE_TEXT$.txt</LogFilename>
        <LogMode>AllPrintableOutput</LogMode>
        <LogOverwriteMode>Append</LogOverwriteMode>
        <LogPathType>Global</LogPathType>
        <PrivateKeyPromptForPassPhrase>false</PrivateKeyPromptForPassPhrase>
        <SSHGateways>
          <SSHGateway>
            <CredentialConnectionID>xxxxxxxxxxxxxxxxxxxxxxxxx</CredentialConnectionID>
            <CredentialSource>CredentialRepository</CredentialSource>
            <Host>xxxxxxxxxx</Host>
            <ID>xxxxxxxxxxxxxxxxxxxxxxxxx</ID>
            <PrivateKeyConnectionID>xxxxxxxxxxxxxxxxxxxxxxxxx</PrivateKeyConnectionID>
            <PrivateKeyType>Link</PrivateKeyType>
          </SSHGateway>
        </SSHGateways>
        <UseSSHGateway>true</UseSSHGateway>
      </Terminal>
      <TerminalMac />
    </Connection>
  </Connections>
  <DatabaseID>xxxxxxxxxxxxxxxxxxxxxxxxx</DatabaseID>
  <Version>2</Version>
</RDMExport>

Based on the above, we attempted to do this custom PowerShell command as a special action:

$connection.Terminal.PrivateKeyPromptForPassPhrase = "false";
$connection.Terminal.SSHGateways.SSHGateway.CredentialConnectionID = "xxxxxxxxxxxxxxxxxxxxx";
$connection.Terminal.SSHGateways.SSHGateway.CredentialSource = "CredentialRepository";
$connection.Terminal.SSHGateways.SSHGateway.Host = "xxxxxxxxxxxxx";
$connection.Terminal.SSHGateways.SSHGateway.PrivateKeyConnectionID = "xxxxxxxxxxxxxxxxxxxxxx";
$connection.Terminal.SSHGateways.SSHGateway.PrivateKeyType = "Link";
$connection.Terminal.UseSSHGateway = "true";
$RDM.Save();

The result was this output:

xxxxxxxxxxxxxxxx: 
The property 'CredentialConnectionID' cannot be found on this object. Verify that the property exists and can be set.
At line:2 char:1
+ $connection.Terminal.SSHGateways.SSHGateway.CredentialConnectionID =  ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo: InvalidOperation: (:) [], RuntimeException
The property 'CredentialSource' cannot be found on this object. Verify that the property exists and can be set.
At line:3 char:1
+ $connection.Terminal.SSHGateways.SSHGateway.CredentialSource = "Crede ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo: InvalidOperation: (:) [], RuntimeException
The property 'Host' cannot be found on this object. Verify that the property exists and can be set.
At line:4 char:1
+ $connection.Terminal.SSHGateways.SSHGateway.Host = "xxxxxxxxxxxx" ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo: InvalidOperation: (:) [], RuntimeException
The property 'PrivateKeyConnectionID' cannot be found on this object. Verify that the property exists and can be set.
At line:5 char:1
+ $connection.Terminal.SSHGateways.SSHGateway.PrivateKeyConnectionID =  ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo: InvalidOperation: (:) [], RuntimeException
The property 'PrivateKeyType' cannot be found on this object. Verify that the property exists and can be set.
At line:6 char:1
+ $connection.Terminal.SSHGateways.SSHGateway.PrivateKeyType = "Link";
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo: InvalidOperation: (:) [], RuntimeException

I've done large batch edits using this process before and it's always worked, so I figure I am missing something here. After staring at and troubleshooting this for a little too long I figured I'd see if any fresh, more expert eyes might be able to point me in the right direction.

Attached is also a screenshot of the above output, as well as our running version.

Thank you!

--
Griffeth Barker