Google indexing alias domain and getting rid of indexed links

See more:

Google

DevExpress

We are facing issues with our Alias domain having been indexed on Google and would like to remove it from Google searches as quickly as possible.

Our main domain is available for the public. Since our site uses Cloudflare and Ezoic, we us an alias domain to make site edits without conflict of Cloudflare and Ezoic caching. Our alias site is only supposed to be available for our development team to make edits. Being it is an alias domain, it has the same root directory and code as our Main site, except it does not serve Ezoic ads.

Despite having set up a canonical tag on the Alias domain, we have recently noticed that Google has indexed our Alias site.

Now we are concerned our traffic has been diluted and our site will or has been penalized for duplicate content. Being our Alias site does not serve ads, we also suspect we have lost ad revenue from visitors going to our Alias site. We want to remove our Alias site from Google indexing as quickly as possible. What is fastest and most efficient method for doing that?

What I have tried:

we have followed the guidelines at https://www.texelate.co.uk/blog/dynamic-automatic-robotstxt-file-with-php-and-htaccess and added following code in .htaccess file

RewriteEngine on RewriteRule ^robots.txt$ /robots.php [L]

Than we added robots.php with a condition to show different robots code for both our Main and Alias domains

Our Main Domains will show our usual robot file whereas the new conditional robot files at our Alias stie will hopefully now prevent all Google bots from indexing our site.