Its easy with the below package, Just install the package via composer :

https://github.com/spatie/array-to-xml

The implementation will be :

$array= 'invoice' => [
    'date' => date('Y-m-d H:i:s'),
    'due_date' => date('Y-m-d H:i:s'),
    'client' => ['name' => 'John', 'code' => ''],
    'items' => [
        'item' => [
            'name' => 'reg1',
            'description' => 'reg1 on evt',
            'unit_price' => '10',
            'quantity' => '1.0'
        ],
        'item' => [
            'name' => 'reg1',
            'description' => 'reg1 on evt',
            'unit_price' => '10',
            'quantity' => '1.0'
        ]
    ]
]

And then :

$result = ArrayToXml::convert($array);

Don't forget to include use Spatie\ArrayToXml\ArrayToXml; at the top of the class/Controller.

Passing an empty array for that element should do the trick:

(new Spatie\ArrayToXml\ArrayToXml([
     'valore1' => 'ciao',
     'valore2' => [], // <===============
]))->prettify()->toXml();