How to do a redirect on the page ( to get rid of Re-submitting the form ) and print the error?

There is a registration form, after it failed to fill ( e.g. left blank, or the username has already been found ), after sending the page, when you try to update it POPs up a window of type "submit data".
How to make so that when you try to refresh the page, the window does not pop up and display the error.
class RegisterController extends AppController
 public function indexAction()
 if(isset($_POST['do_register'])) {
 $registerObj = new RegisterUser();
 $errors = $registerObj->checkUser($_POST, $_FILES);
 if(empty($errors)) {
 $registerObj->registerUser($_POST, $_FILES); // if no errors registered

 }else {
 $this->setData(compact("errors")); // if the error is - pass in, if you posivite header("Location: ... ") before or after this line, the error will not be displayed. 

How to solve this problem?
To get rid of the "Powercity resend form" and bring the error.
April 4th 20 at 13:03
2 answers
April 4th 20 at 13:05
Type in the address bar of your browser to do a redirect and display the error?
April 4th 20 at 13:07
How to solve this problem?

For a start unload back from the trolls and do a primary verification on the client side.
Recommended for reading:
Validation of form data

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