wp editor – wp_editor not working as expected

I have created created a textarea with wp_editor and i want to update the content using wp_post_update.

The problem is that when i try and update the content it removes everything that is already there.

I have tested it with a normal textarea and it works as expected.

The other thing, if i call post_id and insert it into the content it updates.

I hope someone can shed some light on why this is happening.

EDIT: Here is the code:

<?php   

$editor_id = 'update_business_content';
wp_editor( $bio, $editor_id );
                        
if (isset($_POST('btn-update-content'))){
 global $post;

 $new_content = $_POST($editor_id);
 $update = array (
  'ID' => $post_id,
  'post_title' => $name,
  'post_content' => $new_content
 );
                            
 wp_update_post($update);
}                       
?>

HTML Code
The text area in the form is one I created to make sure that the wp_update() was working.

<form method="POST" id="update-content" name="update-content" >
<textarea id="update-test" name="update-test"></textarea>
<button id="btn-update-content" name="btn-update-content" 
>Update</button>
</form>