Custom validation errors aren't showing but the default errors are

I'm trying to get the custom validation error messages to show up on my form.

I have defined the error messages inside the $validationMessage array of my model class 'Post' and it seems that the default ones are appearing.

I have even written stupid code like this to get it to work and they still don't

PHP Code:

    public function store()
    {
        $postModel = new Post();
        $rules = $postModel->validationRules;
        $postModel->setValidationMessages($postModel->validationMessages);
        
        if($this->request->getMethod() == 'post' && $this->validate($rules)) {

            $postModel->save([
                'title' => $this->request->getPost('title'),
                'content' => $this->request->getPost('content')
            ]);

        } else {
            $postModel->setValidationMessages($postModel->validationMessages);
            echo view('templates/header');
            echo view('posts/create-form', ['validator' => $this->validator ]);
            echo view('templates/footer');

        }
    } 


What am I doing wrong here?

Additionally (this could be another for another post) if I call:

PHP Code:

$postModel->errors() 


I get this error:

PHP Code:

Call to a member function lastErrorCode() on bool 


Why is this?