Magento Security Scan not able to verify site
I faced the same issue. This issue seems to be from portal itself.
You can verify the code is added in your site from your browser by looking the source code of your website. search the code if you find the code simply submit the form in the portal. This will add your site and then you can run your scan by selecting the run scan from action column.
We are seeing often this problem coming from web server/proxy/cache removing comments from the output before sending to the browser. If comment with verification ID is removed, the verification will not be successful. The current suggestion is to work with your hosting provider to disable comment removal but Magento will try to enable alternative site verification, eg through meta tags.
I have successfully completed the ownership of the site. I have copied and pasted the conformation code as it is in "HTML Head(Miscellaneous Scripts)" and click on save config. then i have click on "Verify Confirmation code" its working