Why Your Laravel + Inertia.js Fetch Requests Fail with 419 After Save

After a save or reset action, clicking "Preview" returns a 419 Page Expired — even though the page looks fine and you're clearly authenticated. Here's why, and the two-line fix. The Setup A settings page uses Inertia.js for save/reset (router.patch / router.delete) and a plain fetch() POST for a live email preview endpoint. The fetch manually reads the CSRF token from the meta tag: headers: { 'X-CSRF-TOKEN': (document.querySelector('meta[name="csrf-token"]') as HTMLMetaElement)?.content ??...