(Error:400 Bad Request) in codeigniter after resubmitting the form

Question

I am working on a project where all the data is stored as cookies instead of sessions and it is working well but I have some pages where I used the form to post data to the server and whenever I post the multipart form i.e., for eg.,

<? 
   $attr = array('name' => 'form_name', 'id' => 'form_name');
   echo form_open_multipart('form_submit', $attr); 
   some html inputs...
   echo form_close();
?>

The form is getting submitted through controller and after successfully submitted and performed operations I am redirecting to the previous page itself some successful responses but when I reload the page using F5 I am getting a 400 Bad Request error stating "Your browser sent a request that this server could not understand." and "Apache/2.4.41 (Win64) OpenSSL/1.1.1c PHP/7.3.11 Server at localhost Port 80". Can you help me out?

I already went through Bad Request, Your browser sent a request that this server could not understand but couldn't get the solution. Hoping for help!