- array_sum: documentation ( source)
- array_column: documentation ( source)
<?php
$array = [
"list" => [
[
"id" => 1,
"card_id" => 6,
"amount" => 400,
],
[
"id" => 2,
"card_id" => 3,
"amount" => 500,
]
]
];
echo array_sum(array_column($array["list"], 'amount'));