ERROR: Your file appears to be an HTML page

Hello,

We apologize for the inconvenience you are facing with the "Your file appears to be an HTML page" error after installing Rank Math.

To resolve this issue, please ensure that you have submitted the correct XML sitemap to Google. You should submit the sitemap available on your website at https://domain.com/sitemap_index.xml.

If you have confirmed that the correct URL is submitted and you are still encountering the error, you can check for a plugin conflict using the Health Check plugin as mentioned in our guide: Check Plugin Conflicts.

Additionally, if you are using W3 Total Cache along with Rank Math, create another user agent group and add the ‘googlebot‘ user agent to it. You can find more details on how to do this here.

If the above solutions do not resolve the issue, you can include the following filter in your theme’s rank-math.php file:

add_filter( 'rank_math/sitemap/enable_caching', '__return_false');

By adding this filter, you can disable caching for the sitemap and potentially resolve the error.

If you need further assistance or the issue persists, please feel free to reach out to our support team by submitting a ticket here. We are here to help you with any Rank Math-related concerns to ensure a smooth experience with our plugin.

Thank you for your understanding and cooperation.

Sources:
Rank Math Sitemap Issues and Their Fixes » Rank Math
This Plugin Does Not Work with Your Version of PHP » Rank Math
How to Fix "Incorrect HTTP Header Content-Type" Error in Sitemaps » Rank Math