Error message accessing wp-admin.xxx

Can I have your assistance, please?

Once I have completed the Setup Online in the plugin I can log on to the login page for wp-admin.sembec.com.au but not login.

When I try to login I get ‘Sorry, you are not allowed to access this page’.

The URL is showing as

http://wp-admin.sembec.com.au/wp-admin/options-general.php?page=full-site-cache-kc&setup=yes

The background is sembec.com.au is an addon domain on Siteground with wp-admin.sembec.com.au added as a subdomain

Both WordPress installs are hosted on VPS using ServerPilot.

Thanks