Fedex MPS integration in php - php

Question

$client = new SoapClient($path_to_wsdl, ['trace' => 1]);
$this->packageLineItem = [['SequenceNumber'=>1,
'GroupPackageCount' => 1,
'MasterTrackingId' => '123123123123',
'TotalShipmentWeight' =>['Value' => '256', 'Units' => 'LB'],
'Weight' => ['Value' => 1, 'Units' => 'LB'],
],
['SequenceNumber'=>2,
'GroupPackageCount' => 1,
'MasterTrackingId' => '123123123123',
'TotalShipmentWeight' =>['Value' => '256', 'Units' => 'LB'],
'Weight' => ['Value' => 1, 'Units' => 'LB'],
],
['SequenceNumber'=>3,
'GroupPackageCount' => 1,
'MasterTrackingId' => '123123123123',
'TotalShipmentWeight' =>['Value' => '256', 'Units' => 'LB'],
'Weight' => ['Value' => 1, 'Units' => 'LB'],
],
['SequenceNumber'=>4,
'GroupPackageCount' => 1,
'MasterTrackingId' => '123123123123',
'TotalShipmentWeight' =>['Value' => '256', 'Units' => 'LB'],
'Weight' => ['Value' => 1, 'Units' => 'LB'],
]
];
$i = 0;
foreach ($this->packageLineItem as $key => $value)
{
$request = [
'WebAuthenticationDetail' => $this->WebAuthentication,
'ClientDetail' => $this->ClientDetail,
'TransactionDetail' => $this->TransactionDetail,
'Version' => $this->Version,
'RequestedShipment' => [
'ShipTimestamp' => date('c'),
'DropoffType' => 'REGULAR_PICKUP',
'ServiceType' => $ServiceType,
'PackagingType' => 'YOUR_PACKAGING',
'Shipper' => $this->Shipper,
'Recipient' => $this->Recipient,
'ShippingChargesPayment' => $this->ShippingChargesPayment,
'LabelSpecification' => $this->LabelSpecification,
'PackageCount' => 10,
'MasterTrackingId' => '123123123123',
'PackageDetail' => 'INDIVIDUAL_PACKAGES',
'RequestedPackageLineItems' => $value
]
];
print_r($request);
$response = $client->processShipment($request);
print_r($response);
$i++;
}
This code only works for the first piece of the shipment. It prints one label but after that it gives me error "Master Tracking ID invalid". I need to print label for each piece of that shipment. Does any one has any idea about that?