fetchRates

I have two requests
1.
'{"from":{"company":"Test Supplies","address1":"Test street ","city":"Test city","state":"ON","country":"CA","zip":"XXXXXX"},"to":{"company":null,"address1":"1437 C\u00f4te Joyeuse","city":"St Apollinaire","state":"QC","country":"CA","zip":"XXXXX"},"currency":"CAD","unit":"METRIC","expectedShipDate":"XXXXXX","packageType":"PACKAGE","storeIdentifier":"example.info","packages":[{"shopifyProductId":8591,"shopifyVariantId":0,"weight":0,"quantity":1},{"shopifyProductId":8561,"shopifyVariantId":0,"weight":0,"quantity":49}]}'

2.
'{"from":{"company":"Test Supplies","address1":"Test street ","city":"Test city","state":"ON","country":"CA","zip":"XXXXXX"},"to":{"company":null,"address1":"1437 C\u00f4te Joyeuse","city":"St Apollinaire","state":"QC","country":"CA","zip":"XXXXX"},"currency":"CAD","unit":"METRIC","expectedShipDate":"XXXXXX","packageType":"PACKAGE","storeIdentifier":"example.info","packages":[{"shopifyProductId":8591,"shopifyVariantId":0,"weight":0,"quantity":1},{"shopifyProductId":8561,"shopifyVariantId":0,"weight":0,"quantity":50}]}'

the only difference between them is the quantity of the product.

At the first request it returns rates, but at the second nothing

1. 

array (
'response' =>
(object) array(
'data' =>
(object) array(
'rates' =>
array (
0 =>
(object) array(
'serviceName' => 'Standard',
'carrierName' => 'UPS',
'serviceCode' => '604',
'totalCharge' => 85.43,
'estTransitDays' => '2',
'description' => 'Rate details',
'currency' => 'CAD',
),
1 =>
(object) array(
'serviceName' => 'Ground',
'carrierName' => 'Canpar',
'serviceCode' => '4500',
'totalCharge' => 184.31,
'estTransitDays' => '1',
'description' => 'Rate details',
'currency' => 'CAD',
),
2 =>
(object) array(
'serviceName' => 'Expedited',
'carrierName' => 'UPS',
'serviceCode' => '601',
'totalCharge' => 1018.01,
'estTransitDays' => '2',
'description' => 'Rate details',
'currency' => 'CAD',
),
3 =>
(object) array(
'serviceName' => 'UPS Saver',
'carrierName' => 'UPS',
'serviceCode' => '607',
'totalCharge' => 1203.01,
'estTransitDays' => '2',
'description' => 'Rate details',
'currency' => 'CAD',
),
4 =>
(object) array(
'serviceName' => 'Express',
'carrierName' => 'UPS',
'serviceCode' => '600',
'totalCharge' => 1585.15,
'estTransitDays' => '2',
'description' => 'Rate details',
'currency' => 'CAD',
),
),
),
'message' => 'Rates fetched successfully',
'success' => true,
),
'httpResponseCode' => 200,
)

2.

array (
  'response' => 
  (object) array(
     'data' => 
    (object) array(
       'rates' => 
      array (
      ),
    ),
     'message' => 'Rates fetched successfully',
     'success' => true,
  ),
  'httpResponseCode' => 200,
)

what could be the matter?