How to fix error "Cannot dispatch middleware Application\Middleware\IndexMiddleware"? - zend-framework

Question

I've set up a Zend Application as normal, except in my case the difference is that I set it up over an existing legacy web application.
I still want to call my existing legacy application over the ZF3 app. It was suggested I can do so using Middleware. I went over https://docs.zendframework.com/zend-mvc/middleware/ and set up my routing as described there.
However, when I run the application, I am greeted by this:
Cannot dispatch middleware Application\Middleware\IndexMiddleware
#0 zend-mvc\src\MiddlewareListener.php(146):
Zend\Mvc\Exception\InvalidMiddlewareException::fromMiddlewareName('Application\\Mid...')
Here is where the exception happens:
https://github.com/zendframework/zend-mvc/blob/release-3.1.0/src/MiddlewareListener.php#L146
Just to note:
$middlewareToBePiped; //'Application\Middleware\IndexMiddleware'
is_string($middlewareToBePiped); // true
$serviceLocator->has($middlewareToBePiped);//false
$middlewareToBePiped instanceof MiddlewareInterface; //false
is_callable($middlewareToBePiped);//false
My class is:
namespace Application\Middleware;
use Psr\Http\Message\ResponseInterface;
use Psr\Http\Message\ServerRequestInterface;
use Interop\Http\ServerMiddleware\MiddlewareInterface;
use Interop\Http\ServerMiddleware\DelegateInterface;
use Zend\Http\Response;
class IndexMiddleware implements MiddlewareInterface
{
public function __invoke(ServerRequestInterface $request, ResponseInterface $response)
{}
public function process(ServerRequestInterface $request, DelegateInterface $delegate)
{}
}
I am thinking that my issue is that my IndexMiddleware class is not being found in ServiceLocator... (line 142 of linked API). How do I get it in there?

Answer 1

I put this into my application.config.php file:
'service_manager' => [
'invokables' => array(
'middleware' => IndexMiddleware::class
)
]
onto the next error it is.. (Last middleware executed did not return a response.)
but looks like it has executed)