WordPress: a current release (the plugin is tested with the latest WordPress); PHP 7.4 or newer, PHP 8.x recommended.
WooCommerce: optional. Without it the plugin sells vouchers through its own forms and payment gateways; with it you can additionally sell gift cards as WooCommerce products and redeem vouchers in the WooCommerce cart and checkout, including the Cart and Checkout Blocks.
Multisite: supported; activate the plugin per site.
Multilingual: WPML and Polylang are supported (e.g. separate success pages per language); translations for 13 languages are included.
Cron: scheduled deliveries and email retries run through WP-Cron. On busy or low-traffic sites set up a real server cron that calls wp-cron.php every few minutes.
PDF: vouchers, receipts and invoices are generated on your server; no external service is needed. Make sure wp-content/uploads is writable.