How to upload an image to a wordpress site?

Question

WordPress

Function file:

add_action( 'after_setup_theme', 'theme_register_nav_menu' );
function theme_register_nav_menu() {
    add_theme_support( 'post-thumbnails', array( 'post' ) );
}

Post Image File:
<?php the_post_thumbnail('thumbnail') ?>

A new "Post Image" panel appears in post editing. We go into it, select the file and get an error:

When adding a file to media files, it does not load with the same message. There may be a problem with permissions, but posts, pages, tags and categories are created. Why is it happening and how to fix it?

Answer 1

To correctly upload files, you must give write access to the ./wp-content/uploads folder.
On the local machine, just execute chmod
chmod -R 777 ./wp-content/uploads