"PolicyDefinition": [
    {
      "policyDefinitionId": "/providers/Microsoft.Management/managementGroups/MyMGMT/providers/Microsoft.Authorization/policyDefinitions/Deny-RDP-From-Internet",
      "definitionVersion": "1.*.*",
      "parameters": {
        "effect": {
          "value": "[parameters('RDPAccessEffect')]"
        }
      },
      "policyDefinitionReferenceId": "RDPAccessEffect"
    }, ...
]

$params = @{
	Name                = $PSItem.Name
	DisplayName         = "$($PSItem.DisplayName) v$($PSItem.Version)"
	Description         = $PSItem.Description
	Metadata            = ($PSItem.Metadata | ConvertTo-Json -Depth 50)
	Parameter           = ($PSItem.Parameter | ConvertTo-Json -Depth 50)
	PolicyDefinition    = ($PSItem.PolicyDefinition | ConvertTo-Json -Depth 50)
	ManagementGroupName = $PSItem.ManagementGroupId
}
$null = New-AzPolicySetDefinition @params -ErrorVariable oErr