Example for TradeGecko API which updates the stock levels for the variant.

tradegecko-example.php

<?php
declare(strict_types=1);

use Symfony\Component\HttpClient\HttpClient;
use Symfony\Contracts\HttpClient\ResponseInterface;

/**
 * Using two Composer packages:
 * - symfony/var-dumper
 * - symfony/http-client
 */
require './vendor/autoload.php';

// Try to authorize access token
$token = '';
$url = 'https://api.tradegecko.com/';

$client = HttpClient::create([
    'auth_bearer' => $token
]);

try {
    $product_variant_id = 75577508;
    $stock_to_update_to = 200;

    dump('Vanted stock: ' . $stock_to_update_to);

    // Get product variant current stock
    $response = $client->request('GET', "${url}variants/${product_variant_id}");
    $variant = maybe_json_decode($response)->variant;
    $current_stock = intval($variant->available_stock);
    dump('Current stock: ' . $current_stock);

    if ($current_stock === $stock_to_update_to) {
        dd('Current stock is the same as desired, no need to update');
    }

    // Update stock
    $difference = $stock_to_update_to - $current_stock;

    dump('Difference equals to: ' . $difference);

    // First create stock_adjustment object
    $response = $client->request('POST', "${url}stock_adjustments", [
        'body' => [
            'stock_adjustment' => [
                'company_id' => 61642642, // Create a fake one if needed
                'issued_at' => date('c'),
                'billing_address_id' => 79642685, // Create a fake one if needed
                'shipping_address_id' => 79642685, // Create a fake one if needed
                'stock_adjustment_reason_id' => "1245613" // Create a fake one if needed
            ]
        ]
    ]);

    $stock_adjustment_id = maybe_json_decode($response)->stock_adjustment->id;

    // Then create stock_adjustment_line_item
    // NOTE that you can create multiple stock_adjustment_line_items per single stock_adjustment object
    $response = $client->request('POST', "${url}stock_adjustment_line_items", [
        'body' => [
            'stock_adjustment_line_item' => [
                'quantity' => $difference,
                'variant_id' => $product_variant_id,
                'stock_adjustment_id' => intval($stock_adjustment_id),
            ]
        ]
    ]);

    dump(maybe_json_decode($response)->stock_adjustment_line_item);

    // Get product variant new stock
    $response = $client->request('GET', "${url}variants/${product_variant_id}");
    $variant = maybe_json_decode($response)->variant;
    $current_stock = intval($variant->available_stock);
    dump('New stock: ' . $current_stock);

} catch (Throwable $e) {
    dd($e);
}

/**
 * @param ResponseInterface $response
 * @return object|null
 */
function maybe_json_decode(ResponseInterface $response): ?object
{
    try {
        $validResponse = $response->getContent();
    } catch (Throwable $e) {
        dump($e);
        dd(json_decode($response->getContent(false)));
    }

    return json_decode($validResponse) ?: null;
}