Organize Slim 3 API routes logic into functions - php

Question

I would like structure the API in order to separate both the routing organization from actions in separate files.
The current code does not return any errors, but the parameters are not collected correctly.
Is there a simple way to organize into functions without the need for classes, or __invoke?, the application does not require it.
public/index.php
use \Psr\Http\Message\ServerRequestInterface as Request;
use \Psr\Http\Message\ResponseInterface as Response;
require '../vendor/autoload.php';
$app = new \Slim\App;
foreach (glob("../src/middleware/*.php") as $middleware) {
require $middleware;
}
require '../src/routes/routes.php';
$app->run();
src/routes/routes.php
$app->group('/v1', function () use ($app) {
$app->post('/register', 'registerParticipant');
});
src/middleware/registerParticipant.php
require '../lib/qrlib/vendor/qrlib.php';
function registerParticipant($request, $response, $args) {
// demo for testing
$foo= $request->post('foo');
echo "foo= ".$foo;
// more app logic
}

Answer 1

Replacing $foo= $request->post('foo'); with $foo= $request->getParam('foo'); did the trick.
src/middleware/registerParticipant.php
require '../lib/qrlib/vendor/qrlib.php';
function registerParticipant($request, $response, $args) {
// demo for testing
$foo= $request->getParam('foo');
echo "foo= ".$foo;
// more app logic
}