Laravel Middleware Route Group Problems - php

Question

I'm using: Laravel Framework version 5.1.24 (LTS), and I am having great difficulty with implementing a Middleware route group.
Here is what I have in my routes.php:
Route::group(['middleware' => 'api'], function () {
Route::get('api/users', 'UserController#getUsers');
Route::get('api/user/{id}', 'UserController#viewUser');
Route::post('api/user', 'UserController#addUser');
Route::put('api/user/{id}', 'UserController#updateUser');
Route::delete('api/user/{id}', 'UserController#deleteUser');
});
I've also added this to the $routeMiddleware array within Kernel.php:
'api' => \App\Http\Middleware\ApiAuthenticate::class,
I have the ApiAuthtenticate Middleware set to run before continuing, so I'm expecting to see the error handling I have in there, but I am not. What I do get is the MethodNotAllowedHttpException exception thrown.
The strange thing is if I remove the Middleware route group, and add the ApiAuthenticate class to the $middleware array within Kernel.php, it behaves exactly as it should (throws my Exceptions). However, I want to use the Middleware on a specified group of routes, not on the entire global scope.
Can someone please help?
Here is the Middleware:
namespace App\Http\Middleware;
use Closure;
use Session;
use Symfony\Component\HttpKernel\Exception\BadRequestHttpException;
class ApiAuthenticate
{
public function handle($request, Closure $next)
{
if ($request->header('content-type') != 'application/x-www-form-urlencoded') {
throw new BadRequestHttpException('The request must be: Content-Type: application/x-www-form-urlencoded');
}
return $next($request);
}
From Kernel.php:
protected $middleware = [
\Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode::class,
\App\Http\Middleware\EncryptCookies::class,
\Illuminate\Cookie\Middleware\AddQueuedCookiesToResponse::class,
\Illuminate\Session\Middleware\StartSession::class,
\Illuminate\View\Middleware\ShareErrorsFromSession::class,
//\App\Http\Middleware\VerifyCsrfToken::class,
//\App\Http\Middleware\ApiAuthenticate::class,
];
protected $routeMiddleware = [
'auth' => \App\Http\Middleware\Authenticate::class,
'auth.basic' => \Illuminate\Auth\Middleware\AuthenticateWithBasicAuth::class,
'guest' => \App\Http\Middleware\RedirectIfAuthenticated::class,
'api' => \App\Http\Middleware\ApiAuthenticate::class,
];