If you cannot access your website at the new URL, you need to remove the reference to the old domain name and save the new domain name in the wp-config.php file.
To edit this file, you need to access the webspace with an FTP program or the WebspaceExplorer. You can find the login data for your FTP account in 1&1 IONOS under Hosting > Manage Webspace > Secure FTP Account.
You can then edit the wp-config.php file. Paste the following entries at the end of this file and replace "http://www.new-domain-name.com" with the new URL:
- define('WP_SITEURL', 'http://www.new-domain-name.com');
- define('WP_HOME', 'http://www.new-domain-name.com');
These constants overwrite the entries for the previous URLs in the database. This also applies to the URLs that were defined in the WordPress back-end system.