wp-admin/updatecode.json

There are these core files:
/wp-admin/update.php
/wp-admin/update-core.php

However, there is NO /wp-admin/updatecode.json

I suggest scanning your site:
https://sitecheck.sucuri.net/

What’s the error?

I already told you that file is NOT a WP core file 🙂

If you think you site is compromised, then carefully follow this guide. When you’re done, you may want to implement some (if not all) of the recommended security measures.