a20.php

<?php 
$invoice = [
    "invoiceNumber" => "INV-123",
    "invoiceDate" => "2021-01-01",
    "invoiceItems" => [
        [
            "item" => "item1",
            "quantity" => 2,
            "price" => 100
        ],
        [
            "item" => "item2",
            "quantity" => 3,
            "price" => 200
        ],
        [
            "item" => "item3",
            "quantity" => 4,
            "price" => 300
        ]
    ]
];

echo $invoice['invoiceNumber'];
echo PHP_EOL;
echo "---------------------------------------------------------------";
echo PHP_EOL;
echo $invoice['invoiceDate'];
echo PHP_EOL;
echo "---------------------------------------------------------------";
foreach($invoice['invoiceItems'] as $item){
    // echo $item['item'] . " - " . $item['quantity'] . " - " . $item['price']; //string concatenation
    echo "{$item['item']} - {$item['quantity']} - {$item['price']}";
    echo PHP_EOL;
}
echo "---------------------------------------------------------------";