Make sure you have the php-zip extension installed on your webserver

Check if there is the file "onyx-settings.json" in the root directory of namelessmc (where the folders custom, modules, core are). If there isn't one there, create it (and leave it empty). Also ensure it has the file permission 755. If that doesn't work, try 777.

Change both "upload_max_filesize" and "post_max_size" to 100M in php.ini (contact your host about how to edit this file) and then restart your web server