PHP

<?php

$url = 'https://api.unifyunits.com/v1/convert?value=1&from=ft&to=m';

$ch = curl_init($url);
curl_setopt_array($ch, [
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_HTTPHEADER => [
        'Authorization: Bearer ' . getenv('UNIFYUNITS_API_KEY'),
    ],
    CURLOPT_TIMEOUT => 10,
]);

$response = curl_exec($ch);
$status   = curl_getinfo($ch, CURLINFO_HTTP_CODE);
curl_close($ch);

if ($status < 200 || $status >= 300) {
    $error = json_decode($response, true, 512, JSON_THROW_ON_ERROR);
    throw new RuntimeException($error['error']['code'] . ': ' . $error['error']['message']);
}

$data = json_decode($response, true, 512, JSON_THROW_ON_ERROR);
echo $data['data']['result']['value']; // "0.3048"

<?php

$payload = json_encode([
    'conversions' => [
        ['value' => '10',  'from' => 'kg', 'to' => 'lb'],
        ['value' => '100', 'from' => 'km', 'to' => 'mi'],
    ],
]);

$ch = curl_init('https://api.unifyunits.com/v1/batch');
curl_setopt_array($ch, [
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_POST           => true,
    CURLOPT_POSTFIELDS     => $payload,
    CURLOPT_HTTPHEADER     => [
        'Authorization: Bearer ' . getenv('UNIFYUNITS_API_KEY'),
        'Content-Type: application/json',
    ],
    CURLOPT_TIMEOUT => 10,
]);

$response = curl_exec($ch);
curl_close($ch);
$result = json_decode($response, true, 512, JSON_THROW_ON_ERROR);

foreach ($result['data'] as $item) {
    if ($item['status'] === 'success') {
        echo "Item {$item['index']}: {$item['result']['value']} {$item['result']['unit']}\n";
    } else {
        echo "Item {$item['index']} failed: {$item['error']['code']}\n";
    }
}