Laravel Sail 503 in index.php

I have an install of Laravel running in sail, a mate has the same project (Laravel 9) and it runs fine on his system but on mine I get a 503. The error is occurring at this point in the index.php file…

$kernel = $app->make(Kernel::class);
$response = $kernel->handle(
    $request = Request::capture()
)->send();

I can successfully dd before this block but it falls over with a 503 if I move the dd to be after it.

Any help on where to look would be greatly appreciated.

Gary