Estes - Track by Purchase Order

{
  "carrier": "Estes",
  "action": "track",
  "params": {
    "key": "YOUR_ESTES_API_KEY",
    "username": "YOUR_MYESTES_USERNAME",
    "password": "YOUR_MYESTES_PASSWORD",
    "reference_type": "PO",
    "tracking_number": "PO-554238"
  }
}

<?php
$rs = new RocketShipIt;
$response = $rs->request(
array (
  'carrier' => 'Estes',
  'action' => 'track',
  'params' => 
  array (
    'key' => 'YOUR_ESTES_API_KEY',
    'username' => 'YOUR_MYESTES_USERNAME',
    'password' => 'YOUR_MYESTES_PASSWORD',
    'reference_type' => 'PO',
    'tracking_number' => 'PO-554238',
  ),
)
);

rs.request(
  {'action': 'track',
 'carrier': 'Estes',
 'params': {'key': 'YOUR_ESTES_API_KEY',
            'password': 'YOUR_MYESTES_PASSWORD',
            'reference_type': 'PO',
            'tracking_number': 'PO-554238',
            'username': 'YOUR_MYESTES_USERNAME'}}

)

rs.request(
  {"carrier"=>"Estes",
 "action"=>"track",
 "params"=>
  {"key"=>"YOUR_ESTES_API_KEY",
   "username"=>"YOUR_MYESTES_USERNAME",
   "password"=>"YOUR_MYESTES_PASSWORD",
   "reference_type"=>"PO",
   "tracking_number"=>"PO-554238"}}

)

rocketshipit.request(
  {
  "carrier": "Estes",
  "action": "track",
  "params": {
    "key": "YOUR_ESTES_API_KEY",
    "username": "YOUR_MYESTES_USERNAME",
    "password": "YOUR_MYESTES_PASSWORD",
    "reference_type": "PO",
    "tracking_number": "PO-554238"
  }
}
)