Four Spaces Before <?php

I was working on a Livewire component when every interaction started throwing 419 errors. CSRF token mismatch, on every click. The kind of thing that makes you question your setup immediately.

At first I assumed it was a Livewire issue. But then I noticed something stranger — every page refresh generated a new session ID. Sessions worked fine with php artisan serve, but the moment I switched to Herd, no cookies stuck. Each request was a clean slate.

The 419 errors were just a symptom. Laravel couldn’t maintain sessions because the browser never received a cookie.

Chasing the usual suspects

I started with the .env file:

SESSION_DRIVER=redis
SESSION_LIFETIME=120
SESSION_DOMAIN=null
SESSION_SECURE_COOKIE=false

Redis was running, PHP could connect to it. I created a test route to confirm sessions worked at the PHP level — they did. Data was stored, but the browser never got the Set-Cookie header.

I checked DevTools. No laravel_session cookie. No Set-Cookie header at all.

I went through the usual list: cookie domain, HTTPS settings, session path, Redis connection. All fine. Switched to the file driver. Same result. Tried setting a cookie manually:

Route::get('/cookie-test', function () {
    return response('Test')
        ->cookie('test_cookie', 'test_value', 60);
});

Still no Set-Cookie header. At this point it clearly wasn’t a Laravel config problem. Something was preventing PHP from sending cookies entirely.

The actual problem

The breakthrough came from a raw header() call:

Route::get('/header-test', function () {
    header('X-Custom-Test: working');
    // ...
});

PHP responded with: “Cannot modify header information — headers already sent”, and pointed to routes/web.php:1.

Line 1 should just be <?php. I opened the file and there it was — the tag was indented. Four spaces sitting right there, plain as day. I just hadn’t noticed.

Why it only showed up in Herd

The bug existed all along. php artisan serve has output buffering enabled by default, so those spaces never reached the browser before the headers. The problem was silently masked.

Herd uses nginx + PHP-FPM with output_buffering = 0. Output goes out immediately. Those four spaces hit the browser before Laravel could send any headers — which meant no cookies, which meant no sessions.

The fix

Delete four spaces. That’s it.

I made sure routes/web.php started with <?php on the very first character of the very first line. Saved. Everything worked.

Livewire relies on the session to verify CSRF tokens on every request. Without a Set-Cookie header, the browser never stores a session — and without a session, every Livewire interaction fails with a 419.

Four spaces before <?php were enough to start the response body, and once the body starts, PHP can’t send headers anymore.