Refresh page after WordPress form submission, without 'Confirm Resubmission' alert - php

Question

I have my form doing what it needs to (add/remove tag from post depending on whether it's there or not). But - once I submit the form the page doesn't update as intended, the $buttonTitle doesn't update unless I re-load the page in another tab. If I try to refresh I get the message 'Confirm Form Resubmission', I'm a complete noob to php forms, but here's my code...
<?php
$idTag = $current_user->ID;
$spitOutTag = (string)$idTag;
if (has_tag( $spitOutTag, $post )) {
$buttonTitle = 'REMOVE TAG';
} else {
$buttonTitle = 'ADD TAG';
} ?>
<form name="primaryTagForm" action="<?php echo the_permalink() ?>" id="primaryTagForm" method="POST" enctype="multipart/form-data" >
<fieldset>
<input type="hidden" name="newtags" id="newtags" value="<?php echo $current_user->ID; ?>" />
<?php wp_nonce_field( 'post_nonce', 'post_nonce_field' ); ?>
<button id="btn-join" class="btn btn-lg" type="submit"><?php echo $buttonTitle ?></button>
</fieldset>
</form>
<?php if ( is_user_logged_in() && isset( $_POST['newtags'] ) ) {
if (has_tag( $spitOutTag, $post )) {
// Get all the tags as an array of names
$tags = wp_get_post_tags( get_the_ID(), array('fields' => 'names') );
// Remove the tag from the array
$index = array_search( $idTag, $tags );
unset( $tags[$index] );
// Reset the tags
wp_set_post_tags( get_the_ID(), $tags );
} else {
wp_set_post_tags(get_the_ID(), sanitize_text_field($_POST['newtags']), true );
}
} ?>

Answer 1

The problem is that you're assigning the tags after checking them, that's why the button doesn't change, you'll need to arrange your code like this:
First, checking if some tags were sent and apply it to the post:
<?php if ( is_user_logged_in() && isset( $_POST['newtags'] ) ) {
............
} ?>
Then checking the Button:
if (has_tag( $spitOutTag, $post )) {
$buttonTitle = 'REMOVE TAG';
} else {
$buttonTitle = 'ADD TAG';
} ?>
Finally printing the HTML:
<form name="primaryTagForm" action="<?php echo the_permalink() ?>"
....
</form>