Problem: If you're experiencing issues where the order status changes from processing to completed and the PDF invoice plugin should generate an invoice number, but it does not always work, you might suspect WPML interference as suggested by the Invoice PDF plugin developer. Solution: We have reviewed your site and the WPML and WCML setup, confirming that both plugins are fully initialized and correctly configured. WPML/WCML follows standard WordPress and WooCommerce coding practices, and there is no intentional difference in how order status changes are handled, whether triggered via REST API, webhooks, or standard requests. We are not aware of any cases where WPML fails to load during background or webhook-based requests. To investigate further, enable WordPress debugging to check for any PHP errors during order status changes. We also recommend testing in a controlled environment, such as a local or staging site, using a step-by-step debugger to analyze hook execution in detail. Importantly, tests conducted on a local copy of your site with WPML plugins deactivated showed that the invoice number was not generated after changing the order status, suggesting that WPML may not be the root cause. Additionally, WooCommerce PDF Invoices & Packing Slips Professional is fully compatible with WPML, with no known compatibility issues related to this behavior (https://wpml.org/plugin/woocommerce-pdf-invoices-and-packing-slips-professional/).
If this solution does not resolve your issue or seems irrelevant due to being outdated or not applicable to your case, we highly recommend checking related known issues (https://wpml.org/known-issues/), verifying the version of the permanent fix, and confirming that you have installed the latest versions of themes and plugins. If the problem persists, please open a new support ticket for further assistance at WPML support forum.
