Adsense won’t verify site ownership

I’m having issues with Adsense verifying my site ownership and was wondering if I’m doing something wrong or if it takes time.

I have input the Adsense code under the Heading tab as per the following page (https://adinserter.pro/documentation/adsense-ads#connect-your-site), ensuring that the enable button is green and that I saved it.

Unfortunately when I go to Adsense and click “Verify” under the verify site ownership section, it is still unable to verify anything. I’m not really sure what to do since as far as I can tell I have done everything correct.

Does it take time for the code to be recognized by Google crawlers?