$data = [
    'channel' =>
        [
            'item' => [
                ['product_id' => '1', 'product_name' => 'abc',],
                ['product_id' => '2', 'product_name' => 'def',]
            ];
function datam($data){
$keys=array_keys($data);
return $data[$keys[0]][$keys[1]];
}
$products= datam($data);