Unable to save the last xml file php -

i new php, , have written code work amazon api. when request information api, receive it, unable sort through xml. here error:

fatal error: call member function children() on null in j:\xampp\htdocs\phillip\src\marketplacewebserviceproducts\samples\csv_prep.php on line 117 

here code:

if(is_array($xmlfiles)){     foreach($xmlfiles $xmlfile){     $xml = simplexml_load_file($xmlfile);         foreach($xml->getmatchingproductforidresult $items) {                      //line 117 ->            if(isset($items->products->product->attributesets->children('ns2', true)->itemattributes->listprice->amount) !== false) {                  $amount = $items->products->product->attributesets->children('ns2', true)->itemattributes->listprice->amount             }else{                 $amount = '0.00';             }        }    }  } 

the tag in xml trying value of looks this:

<ns2:amount>9.99</ns2:amount> 

it in same place says in code. have problem large files , not sure happening. if help, appreciate it. in advance!

i'm not certain, based on error message, looks somewhere in $items->products->product->attributesets hierarchy you're specifying not exist.

do tests see if $items or $items->products or $items->products->product or $items->products->product->attributesets , whichever 1 fails, print out fact , call exit;.

you print_r on $items well.