Good news folks. Thanks to @agallou, you can save content from any complicated page (with paywall, client side rendering through API).

• Go to the addon's settings
• add the URL of any site not working with wallabag at the moment on the text box labeled by "Retrieve content from the browser (an URL by line)"
• go to the page you want to save
• click on the wallabagger icon Et voilà ! 🎉