Flashdata not clearing on refresh/redirect

Well,
in your controller:

1- get the data from your view (You can check the link I am leaving for step 2)
2 check if they pass your rules or not (Follow this link)
3- if yes, pass them to model.
4- if not, turn back an error (no need for flashdata).

- - - -

3- If you pass your data to model and to database successfully then you can call your flashdata, like:

PHP Code:

$data = [
  'name' => $name,
  'surname' => $surname,

etc..

];

$result = $this->MyModel->lets_do_sth($data);
if($result){
$this->session->set_flashdata('success_message', 'You did it.');

        redirect('lets_go_to_login');
} 


By the way, why don't you go with CI 4?