use function inside another function in WP Plugin

I tried creating a shortcode in my custom plugin, but in order for it to work, you need to apply a filter that converts all the new shortcodes you created to the content. Where the content is being rendered (like in the single.php file), replace the_content() with
apply_filters('the_content',get_the_content())

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)