gistfile1.php

<?php

$base = "https://www.lootsy.com/api/1.2/catalog?tag=%24f&beforeId=";
$ids = [];
$items = [];

do {
    $beforeId = empty($ids) ? "" : end($ids);
    $url = $base . $beforeId;
    echo "$url\n";
    $json = file_get_contents($url);
    $o = json_decode($json);

    if (empty($o->body)) {
        break;
    }
    
    foreach ($o->body as $item) {
        if (in_array($item->id, $ids)) {
            echo "already have " . $item->id . "\n";
            exit();
        }
        
        $ids[] = $item->id;        
    }
} while (true);