Custom plugin doesn’t show in admin menu – when code added, displays an empty page

It turns out the plugin is not meant to have a page in the administration. It just generates some HTML code from the [uverovakalkulacka] shortcode based on the contents of settings.json which is supposed to be edited manually. Thank you for your time.

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