Powershell AddInterfacesOnNode

I am working on a power shell script to add nodes.  Everything works to add the node except for when I try to call the AddInterfacesOnNode.  When I send the request I get the following error:

Invoke-RestMethod : "Expecting state 'Element'.. Encountered 'Text'  with name '', namespace ''. "

Anyone else run across this error when trying to add an interface using powershell and not the powershell module?

Below is the JSON and the code that I am try to use to get the interface added.

[

    4519,

    {

        "ifIndex":  10101,

        "Caption":  "GigabitEthernet0/1 - Gi0/1",

        "ifType":  6,

        "ifSubType":  0,

        "InterfaceID":  0,

        "Manageable":  true,

        "ifSpeed":  0.0,

        "ifAdminStatus":  0,

        "ifOperStatus":  4

    },

    "AddDefaultPollers"

]

# 
function AddInterfacesOnNode ($nID, $nodeInterface){
$URI = $URL+"Invoke/Orion.NPM.Interfaces/AddInterfacesOnNode/"
 
$intBody = @($nID,$nodeInterface,"AddDefaultPollers")| ConvertTo-Json

$msgBody = $intBody

write-host $msgBody

  $result = Invoke-RestMethod -Uri $URI -Method POST -Body $msgBody -Credential $credential -ContentType "application/json"
  Write-Log -Message "Successfully added interface $properties.caption"  -Severity Information -Details $result
  return $result
}

#