php issue with array push inside of a function, // reference

I want to use array_walk_recursive to extract values of one array and put them into another array. So I did this:

1. Created a multidimensional test array (where you can find 2 keys named "second_key")
2. Created a second array and pushed some test entries
3. Now I want to extract all values of "second_key" and push to the new array But I am facing the issue that it will not work, most likely because of missing reference. Any idea how to fix this?

    <?php
    $test_array = array();
    $test_array['NUMERO_ONE'] = array(
        "initial_key" => "Alpha", 
        "details" => array(
            "first_key" => ".Alpha_1", 
            "second_key" => "Alpha_2"
        )
    );
    $test_array['NUMERO_TWO'] = array(
        "initial_key" => "Beta", 
        "details" => array(
            "first_key" => ".Beta_1", 
            "second_key" => "Beta_2"
        )
    );
    var_dump($test_array);
    echo "<br>***********************************<br>";

    $results_array = array();
    $results_array[] = "banana";
    array_push($results_array, "tomato");
    var_dump($results_array);
    echo "<br>***********************************<br>";


    // ?? $results_array should be a reference, but how??
    // see here: https://stackoverflow.com/questions/20169327/array-push-not-working-within-function-php
    function  my_function($value, $key, &$results_array) {
      echo "Content of $key is: $value <br>";
      if ($key == "second_key") {
        echo "SECOND KEY: " . $value . "<br>";
        $results_array[] = $value;
        // even the next simple test is not working 
        $results_array[] = "test_A";
        // also array_push is not working
        array_push( $results_array, $value);
        }
    }

    array_walk_recursive($test_array,"my_function", $results_array);
    echo "<br>***********************************<br>";
    var_dump($results_array);
    ?>