appwrite/docs/examples/1.8.x/server-php/examples/sites/create-variable.md

<?php

use Appwrite\Client;
use Appwrite\Services\Sites;

$client = (new Client())
    ->setEndpoint('https://<REGION>.cloud.appwrite.io/v1') // Your API Endpoint
    ->setProject('<YOUR_PROJECT_ID>') // Your project ID
    ->setKey('<YOUR_API_KEY>'); // Your secret API key

$sites = new Sites($client);

$result = $sites->createVariable(
    siteId: '<SITE_ID>',
    key: '<KEY>',
    value: '<VALUE>',
    secret: false // optional
);